How to Clean Your Soft Flask
TL;DR - Quick Cleaning Guide
Don't have time to read the full guide? Here's everything you need:
Daily Cleaning (After Every Use)
- Rinse immediately with warm water
- Wash with mild dish soap
- Clean the cap and valve separately
- Dry completely upside down
Deep Cleaning (Weekly)
- Baking soda: 1-2 tbsp in warm water, soak 20 min, rinse
- White vinegar: 1:1 with water, soak 15-30 min, rinse until smell gone
- Cleaning tablets: Drop in warm water, fizz 15-30 min, rinse
Mold Removal
- Disassemble completely (flask + valve + cap)
- Scrub visible mold with soapy water
- Soak in undiluted vinegar for 60 min
- Follow with baking soda soak for 20 min
- Final sanitization with cleaning tablets overnight
Pro Tips
- ✅ Store in freezer — Stops bacteria/mold growth completely
- ✅ Denture tablets — Cheap alternative to Bottle Bright
- ✅ Always clean the valve — It's the dirtiest part
- ✅ Never store wet — #1 cause of mold
When to Replace
- Persistent smell after deep cleaning
- Visible cracks or leaks
- Valve won't seal properly
- Material won't hold shape
Keep reading for detailed instructions, brand-specific guides (Salomon, Hydrapak), and the freezer storage hack that prevents bacteria growth.
Whether you own a Salomon, Hydrapak, Nathan, or any other brand of soft flask, keeping it clean is essential for fresh-tasting hydration and extending your flask's lifespan. This guide covers everything from daily cleaning to deep sanitization, mold removal, and the freezer storage hack that prevents bacteria growth between uses.
Quick Answer: How to Clean a Soft Flask
For daily cleaning: Rinse with warm water immediately after use, wash with mild dish soap, and dry upside down completely.
For deep cleaning: Fill with warm water + 1-2 tablespoons baking soda, shake, let sit 20 minutes, rinse thoroughly.
For mold or stubborn smells: Use white vinegar (1:1 with water), denture tablets, or bottle sterilizing fluid.
Pro tip: Store clean, dry flasks in the freezer to prevent bacteria and mold growth between uses.
Why Regular Flask Cleaning Matters
Every time you drink from your soft flask, you're introducing bacteria from your mouth. Mix that with moisture, warmth, and leftover sports drink residue, and you've created the perfect environment for mold and bacteria to thrive.
According to Salomon's hydration care guidelines, regular cleaning prevents bacterial spread and bad odors, even when only using plain water. The bite valve and cap threads are particularly vulnerable since they're in direct contact with your mouth and trap moisture in hard-to-reach crevices.
Signs your flask needs cleaning:
- Funky or musty smell when you open the cap
- Strange taste in your water
- Visible discoloration or cloudiness
- Black or green spots (mold)
- Slimy feeling inside the flask
How to Clean a Soft Flask After Every Use
This 3-minute routine should happen after every run, hike, or workout. It's the single most important habit for keeping your flask fresh.
Step-by-Step Daily Cleaning
What you'll need: Warm water, mild dish soap, soft sponge or bottle brush
Step 1: Empty and rinse immediately
Don't leave liquid sitting in your flask after exercise. Empty it as soon as you're done and give it a quick rinse with warm water. The longer residue sits, the harder it becomes to remove.
Step 2: Wash with mild soap
Add a small amount of dish soap and warm water. If your flask has a wide mouth (42mm cap), you can reach inside with a soft sponge. For narrow-mouth flasks, swish soapy water around vigorously.
Step 3: Clean the cap and valve
This is where most people go wrong. The cap threads and bite valve harbor the most bacteria because they're in contact with your mouth. Wash these separately with soapy water, making sure to get into all the grooves.
Step 4: Rinse thoroughly
Run clean water through the flask and valve until all soap residue is gone. Leftover soap can affect taste and potentially cause stomach issues.
Step 5: Dry completely
This is critical. Shake out excess water and leave your flask open, upside down, on a drying rack or clean towel. Trapped moisture is the number one cause of mold growth.
Time required: 3-5 minutes
How to Deep Clean a Soft Flask
Deep cleaning should happen at least once a week if you use your flask daily, or after every use if you're using sports drinks, electrolytes, or energy gels.
Method 1: Baking Soda Soak (Best for Odors)
Baking soda is a natural deodorizer that neutralizes smells without harsh chemicals. This method is recommended by multiple brands including HydraPak.
What you'll need: Warm water, 1-2 tablespoons baking soda
Steps:
- Fill your flask with warm (not boiling) water
- Add 1-2 tablespoons of baking soda
- Screw on the cap loosely and shake well
- Let sit for 15-20 minutes
- Shake again, then empty
- Rinse thoroughly with clean water
- Dry completely
Pro tip: For extra scrubbing power, make a paste with baking soda and a small amount of water. Use a bottle brush to scrub stubborn areas, especially the threads and bottom corners.
Method 2: White Vinegar Rinse (Best for Bacteria)
White vinegar has natural antibacterial and antifungal properties. The acidity helps dissolve mineral buildup from hard water and kills bacteria that soap alone might miss.
What you'll need: White vinegar, warm water (1:1 ratio)
Steps:
- Mix equal parts white vinegar and warm water
- Fill your flask with the solution
- Swish around to coat all surfaces
- Let soak for 15-30 minutes
- Empty and rinse thoroughly until vinegar smell is gone
- Dry completely
Important: Don't mix vinegar and baking soda together in your flask. While the fizzing looks impressive, it neutralizes both ingredients and reduces cleaning effectiveness. Use them separately for best results.
Method 3: Cleaning Tablets (Best for Convenience)
Effervescent cleaning tablets like Bottle Bright or HydraPak Cleaning Tablets are specifically designed for hydration equipment. They dissolve grime, remove stains, and eliminate odors with minimal effort.
The denture tablet hack: Here's a money-saving secret from the running community. Denture cleaning tablets (like Polident or Steradent) work just as well as expensive bottle-specific tablets, at a fraction of the cost. One runner noted that "denture tabs and Bottle Bright contain similar active ingredients" such as sodium bicarbonate and citric acid.
What you'll need: 1-2 cleaning tablets (or denture tablets), warm water
Steps:
- Fill your flask with warm water
- Drop in 1 tablet (or 2 for larger flasks or heavy buildup)
- Let fizz and soak for 15-30 minutes
- Empty, rinse thoroughly, and dry
Tip: Use unflavored denture tablets to avoid minty-tasting water on your next run.
Method 4: Baby Bottle Sterilizing Fluid (Best for Sanitization)
For serious sanitization, especially after mold exposure, baby bottle sterilizing fluid (like Milton) is highly effective. This method is recommended by outdoor gear experts and has been proven to eliminate mold and bacteria discoloration.
What you'll need: Sterilizing fluid concentrate, cold water, large bowl
Steps:
- Rinse and wash your flask with dish soap first
- Follow the sterilizing fluid instructions (typically 2 caps per 2L of cold water)
- Disassemble your flask completely (cap, valve, any removable parts)
- Submerge all parts in the solution
- Leave overnight for best results
- Rinse thoroughly the next day
- Dry completely before storing
How to Clean a Soft Flask Valve (Bite Valve Deep Clean)
The bite valve is the dirtiest part of your soft flask. It's in direct contact with your mouth, and moisture gets trapped inside the tiny crevices. If you've never cleaned your valve properly, you might be surprised what's growing in there.
How to Disassemble Your Valve
Most soft flask valves can be taken apart for thorough cleaning. Here's how:
For standard bite valves (HydraPak, Salomon style):
- Grasp the bite valve in one hand and the tube/cap in the other
- Pull firmly to separate the valve from the cap
- Gently remove the silicone sheath from the valve body
- You should now have 2-3 separate pieces
For screw-cap flasks with press-fit valves:
- Hold the cap firmly
- Pull the bite valve firmly away from the cap
- Be careful not to lose the small plug or gasket
Cleaning the Disassembled Valve
What you'll need: Warm soapy water, small brush (pipe cleaner, straw brush, or dedicated valve brush), cleaning tablets (optional)
Steps:
- Soak all valve pieces in warm soapy water for 5 minutes
- Use a small brush to scrub inside the valve body
- Clean the silicone sheath thoroughly (mold loves to hide here)
- For stubborn grime, soak in cleaning tablet solution for 15-20 minutes
- Rinse all parts thoroughly
- Allow to dry completely before reassembling
Critical warning: If you don't clean the silicone tip of your valve regularly, residue can eat into the silicone permanently. At that point, you'll need to replace the entire valve. Hydrapak sells replacement sheaths specifically for this reason.
When to Replace Your Valve
Replace your bite valve every 6-12 months depending on usage, or immediately if you notice:
- Persistent bad taste even after cleaning
- Visible cracks or tears
- The valve no longer seals properly
- Discoloration that won't come out
How to Remove Mold From a Soft Flask
Found black or green spots in your flask? Don't panic, and don't throw it away. Mold can usually be removed completely with the right approach.
Emergency Mold Removal Protocol
What you'll need: White vinegar, baking soda, cleaning tablets or sterilizing fluid, bottle brush
Step 1: Assess the damage
Check the entire flask, cap, valve, and any straws or tubes. Mold spreads, so if you see it in one place, assume it's everywhere.
Step 2: Disassemble completely
Take apart every removable component. You cannot effectively clean mold without accessing all surfaces.
Step 3: Initial scrub
Using warm soapy water and a brush, scrub away all visible mold. This removes the bulk but doesn't sanitize.
Step 4: Vinegar soak
Fill with undiluted white vinegar and let sit for 60 minutes. Vinegar kills most mold species and prevents regrowth.
Step 5: Baking soda follow-up
After rinsing the vinegar, do a baking soda soak for 20 minutes. This neutralizes any remaining vinegar and provides additional deodorizing.
Step 6: Final sanitization
For peace of mind, do a final soak with cleaning tablets or sterilizing fluid overnight.
Step 7: Complete dry
This step is non-negotiable. Any remaining moisture will allow mold to return. Dry upside down for at least 24 hours, or use the freezer storage method below.
The Rice Scrubbing Method
For stubborn residue that brushes can't reach, try this technique recommended by Hunting Waterfalls:
- Add a handful of dry rice to your flask
- Add a small amount of dish soap or vinegar and some water
- Put the cap on and shake vigorously for 2-5 minutes
- The rice acts as an abrasive, scrubbing areas you can't reach
- Empty, rinse thoroughly, and dry
How to Clean a New Soft Flask (First Use)
New soft flasks can have a slight plastic taste or manufacturing residue. Here's how to prepare a brand new flask for its first use.
Simple method:
- Rinse with warm water
- Wash with mild dish soap
- Rinse thoroughly
- Fill with water, let sit for a few hours, then empty
- Ready to use
If plastic taste persists:
- Mix warm water with 1 tablespoon lemon juice
- Fill the flask and let soak overnight
- Rinse and wash with soap
- The acidity neutralizes manufacturing residue
Or use the baking soda method:
- Fill with warm water + 2 tablespoons baking soda
- Shake and let sit overnight
- Rinse thoroughly
Some runners prefer to do both: lemon juice soak first, then baking soda soak, with a thorough rinse between each.
The Freezer Storage Hack
Here's a game-changing tip that many runners swear by: store your clean, dry soft flask in the freezer between uses.
Why It Works
Freezing temperatures (0°F / -18°C) halt bacterial and mold growth completely. According to the USDA, freezing inactivates microbes including bacteria, yeasts, and molds. While it doesn't kill them, it stops them from multiplying.
This means a clean flask stored in the freezer stays clean indefinitely, as bacteria and mold can't grow in frozen conditions.
How to Do It
- Clean your flask using any of the methods above
- Ensure it's completely dry (this is essential)
- Leave the cap slightly open or store cap separately
- Place in your freezer
- When ready to use, remove from freezer and it's ready to fill
Note: Don't freeze a flask that still has water in it. The expansion can damage the material. The flask should be empty and dry before freezing.
This method is particularly useful for soft flasks you don't use every day, or for storing flasks between race seasons.
How to Clean a Salomon Soft Flask
Salomon soft flasks are some of the most popular among trail runners. Here are brand-specific tips:
Salomon's official recommendations:
- Top-rack dishwasher safe (remove valve first)
- Hand wash with mild soap and warm water
- Store clean and completely dry
- Store in the freezer to prevent bacteria growth
For the valve:
- Remove the valve from the cap
- Clean with warm soapy water
- Use a small brush for the interior
- Rinse thoroughly
- Allow to air dry completely
Speed caps vs standard caps:
- Speed caps have more components and require more attention
- Disassemble fully for deep cleaning
- Check the silicone gasket for trapped moisture
How to Clean a Hydrapak Soft Flask
HydraPak makes some of the most well-designed soft flasks for cleaning. Here are their specific recommendations:
What makes Hydrapak easier to clean:
- Many models are fully reversible (can be turned inside out)
- Wide mouths accommodate bottle brushes
- Valve components are designed to separate
To reverse your Hydrapak flask:
- Reach inside the flask
- Grab the bottom
- Pull it back through the opening (like turning a sock inside out)
- You can now scrub the interior directly
HydraPak cleaning products:
- Bottle Bright tablets (15-30 minute soak)
- HydraPak Cleaning Kit (brush + tablet)
- Tube Brush for valve cleaning
Soft Flask Cleaning Mistakes to Avoid
❌ Mistake 1: Using bleach
Bleach can damage the TPU material that most soft flasks are made from. It can also leave a residue that's nearly impossible to rinse out completely. Some users report that bleach killed weaker molds but allowed stronger ones to survive. Stick to vinegar, baking soda, or cleaning tablets instead.
❌ Mistake 2: Using boiling water
TPU (thermoplastic polyurethane) can deform at high temperatures. Warm water is fine, but boiling water can warp your flask and damage the seals. Most manufacturers recommend maximum temperatures around 60°C (140°F).
❌ Mistake 3: Storing wet
This is the number one cause of mold and bacterial growth. Always ensure your flask is completely dry before storing. If you're in a rush, the freezer method works for damp flasks too, as the cold prevents growth until you can dry it properly.
❌ Mistake 4: Forgetting the valve
The bite valve is the dirtiest part of your flask. If you only clean the flask body, you're leaving the worst contamination untouched. Always disassemble and clean the valve separately.
❌ Mistake 5: Using abrasive scrubbers
Steel wool or harsh scrub pads can scratch the interior of your flask. Scratches create tiny grooves where bacteria can hide, making future cleaning harder. Stick to soft sponges and bottle brushes.
❌ Mistake 6: Storing with the cap sealed
A sealed flask traps moisture inside, even if you think it's dry. Store with the cap off or loosely placed to allow air circulation.
Soft Flask Cleaning Schedule
Here's a practical schedule based on how you use your flask:
After every use:
- Rinse immediately
- Wash with soap
- Dry completely (or freeze)
Weekly (if using daily):
- Deep clean with baking soda or vinegar
- Clean valve components
- Check for any odors or discoloration
Monthly:
- Full sanitization with cleaning tablets or sterilizing fluid
- Inspect valve for wear
- Check flask material for damage
After using sports drinks or gels:
- Deep clean immediately after use
- The sugars and acids in these products accelerate bacterial growth
After illness:
- Full sanitization before next use
- Consider replacing the valve
Soft Flask Cleaning Supplies Checklist
Essential supplies:
- ☐ Mild dish soap
- ☐ Bottle brush (soft bristles)
- ☐ Small brush for valve (pipe cleaner or straw brush)
- ☐ Drying rack or clean towel
- ☐ Baking soda
- ☐ White vinegar
Optional but helpful:
- ☐ Cleaning tablets (Bottle Bright, HydraPak, or denture tablets)
- ☐ Baby bottle sterilizing fluid (Milton or similar)
- ☐ Dedicated valve brush
- ☐ Drying stand with air circulation
Frequently Asked Questions
How often should I clean my soft flask?
Rinse after every single use and wash with soap daily if using regularly. Deep clean weekly with baking soda or vinegar. Full sanitization monthly or whenever you notice odors.
Can I put my soft flask in the dishwasher?
Most soft flasks are top-rack dishwasher safe, but check your manufacturer's instructions. Always remove the valve before dishwashing, and avoid high-heat drying cycles which can warp the material.
How do I remove a bad smell from my soft flask?
Start with a baking soda soak (1-2 tablespoons in warm water for 20 minutes). If that doesn't work, try white vinegar (1:1 with water for 30 minutes). For persistent smells, use cleaning tablets or sterilizing fluid overnight.
Can I use bleach to clean my soft flask?
It's not recommended. Bleach can damage TPU material and leave residue that's hard to rinse out. It can also harm the silicone valve components. Use vinegar, baking soda, or cleaning tablets instead.
Why does my soft flask still taste bad after cleaning?
Residual odors often live in the valve, not the flask body. Disassemble and clean the valve thoroughly. Also ensure you're drying completely. If problems persist, the silicone may be permanently compromised and need replacing.
How do I clean a soft flask with a narrow opening?
Use the swishing method: fill with soapy water, cap it, and shake vigorously. For deep cleaning, the rice method works well (dry rice + soap + water, shake vigorously). Cleaning tablets are also ideal for narrow-opening flasks.
Can I freeze my soft flask to kill bacteria?
Freezing doesn't kill bacteria, but it stops them from growing. A clean flask stored in the freezer will stay clean. An already-moldy flask needs to be cleaned first, as the mold will simply become dormant (not dead) in the freezer.
How do I clean the bite valve on my soft flask?
Remove the valve from the cap, separate the silicone sheath from the body, clean each piece with warm soapy water and a small brush, rinse thoroughly, and dry completely before reassembling.
What's the best way to dry a soft flask?
Shake out excess water, then store upside down with the opening facing down to let remaining water drip out. Leave the cap off to allow air circulation. A dedicated bottle drying rack with air holes works best. Alternatively, store clean flasks in the freezer.
How long do soft flasks last?
With proper cleaning and care, quality soft flasks last 2-5 years. Signs it's time to replace: persistent odors after cleaning, cracks or leaks, material that won't hold its shape, or damaged valves that won't seal.
Can I put hot drinks in my soft flask?
Most soft flasks are rated for temperatures up to 60°C (140°F). Hot coffee or tea is generally fine, but boiling liquids can damage the material. Check your manufacturer's specifications.
How do I remove mineral buildup from hard water?
White vinegar is excellent for dissolving mineral deposits. Soak with undiluted vinegar for 30-60 minutes, then scrub with a soft brush and rinse thoroughly.
What Our Customers Say About Flask Cleaning
"I've been using the Softflask at the gym, and it has made staying hydrated incredibly easy and hassle-free. The opening is large enough to add my pre-workout without any mess, and once sealed, it doesn't leak at all." — Willco
"Portable and a great option for long runs and marathons. I like the fact that once it's empty, I can easily just fold it and put it in my pocket." — Zina Ndabeni
"One of the best water bottles I have ever owned. Not only does it magically make me drink more water. It makes it fun at the same time." — William
The Bottom Line
Cleaning your soft flask doesn't have to be complicated. The key habits are simple:
- Rinse immediately after every use
- Wash with soap daily
- Deep clean weekly with baking soda or vinegar
- Always dry completely (or use freezer storage)
- Don't forget the valve — it's the dirtiest part
By following these practices, your soft flask will stay fresh, odor-free, and safe to drink from for years. A few minutes of maintenance after each use prevents hours of scrubbing mold later.
Happy running, and stay hydrated!
Looking for a soft flask that's easy to clean? Check out our OG SoftFlask with its wide 42mm cap, or our Mini T SoftFlask for shorter runs.