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A carpet cleaner has two tanks, and both of them get dirty. The clean-water tank holds water and formula. The dirty-water tank holds everything the machine sucked out of your carpet — dirty water, pet hair, crumbs, and bacteria. Leave either tank uncleaned and the next time you use the machine, you are cleaning with dirty water, or blowing a musty smell across a freshly cleaned carpet.
This guide covers how to clean a carpet cleaner tank — both tanks, step by step — plus how to dry them, how often to do it, and the mistakes that cause smells, mold, and clogs.
The Short Answer
Clean both tanks after every use. Empty the dirty-water tank into the toilet, rinse it with warm water until the water runs clear, and let it air-dry with the cap off. Rinse the clean-water tank with warm water, wipe it out, and let it dry too — never store it with formula or water left inside. Once a month, wash both tanks with warm water and a drop of dish soap, rinse thoroughly, and dry completely before reassembling. A tank that is fully dry before storage will not smell, grow mold, or clog.
Know Your Two Tanks
Most carpet cleaners have two separate tanks, and they need different care:
- Clean-water tank: Holds clean water mixed with cleaning formula. It stays relatively clean, but formula residue builds up on the walls and the cap, and any water left inside goes stale and grows mildew.
- Dirty-water tank: Holds the dirty water the machine recovers from the carpet. This is the tank that smells. It collects hair, grit, and organic matter, and it needs cleaning after every single use — no exceptions.
Some machines, like the BISSELL ProHeat 2X Revolution Pet Pro, use a two-tank system where clean water and formula stay separate from dirty water so you are never cleaning with dirty water. Others, like the Hoover PowerDash Pet, use a 0.5-gallon clean-water tank with a separate recovery tank. Whatever your machine’s design, the rule is the same: empty both tanks, rinse both tanks, dry both tanks.
Step 1: Empty the Dirty-Water Tank
Do this right after you finish cleaning, while the contents are still liquid. Dirty water left in the tank settles, dries into a film, and smells worse the longer it sits.
- Turn the machine off and unplug it.
- Remove the dirty-water tank — usually a release latch or a lift-out handle on the front or side.
- Carry it to the toilet and pour the contents in. Do not pour it down a kitchen sink, where food debris can clog the drain.
- If the tank has a float or a filter screen inside, remove it and rinse it separately. Hair and grit collect around the float and stop it working.
Never leave a full dirty-water tank overnight. One night is enough for the smell to set into the plastic.
Step 2: Rinse the Dirty-Water Tank
- Fill the tank about a third full with warm water, swirl it, and pour it out. Repeat until the water runs clear — usually two or three rinses.
- If the tank has a narrow neck, use a bottle brush to reach the corners and the bottom seam, where grit collects.
- For a stubborn smell or film, add a drop of dish soap and warm water, swirl, let it sit for ten minutes, then rinse until no soap remains. Do not use bleach or harsh chemicals unless your manual specifically allows them — they can damage seals and leave a residue that ends up on your carpet.
- Rinse the cap, the gasket, and the float separately, and check the gasket for cracks. A cracked gasket leaks dirty water back onto the floor.
Step 3: Rinse the Clean-Water Tank
The clean-water tank is easier, but do not skip it:
- Pour out any leftover water and formula. Never store formula in the tank between uses — it goes stale, leaves a sticky residue, and clogs the spray nozzles.
- Rinse with warm water and swirl. If you can see a film on the walls, add a drop of dish soap, swirl, and rinse until the water runs clear.
- Check the formula cap and the measuring lines for residue, and wipe them clean.
- If your machine mixes formula automatically, run a tank of plain warm water through the machine once, which flushes formula out of the internal lines as well.
Step 4: Dry Both Tanks Completely
Drying is the step people skip, and it is the step that prevents mold. A tank that looks dry on the outside can still be damp inside, and a damp tank stored with the cap on grows mildew within days.
- Leave both tanks upside down on a dish rack or a towel, with the caps off, for at least 12 hours — overnight is best.
- Stand the tanks so air can circulate inside. A tank left upright with the cap on traps moisture.
- Wipe the inside with a clean cloth first if you are in a hurry, then leave the tank open to finish drying.
- Do not reassemble the machine until both tanks are fully dry to the touch inside and out.
Monthly Deep Clean
Once a month, or after cleaning a particularly dirty carpet or a pet accident, give both tanks a deeper clean:
- Wash both tanks with warm water and dish soap, using a bottle brush on the seams and corners.
- Rinse the dirty-water tank with a solution of one part white vinegar to four parts warm water, which cuts soap film and neutralizes odors. Rinse again with plain water.
- Clean the hose and the brushroll while you are at it — a clean tank does not help if the hose is full of old dirty water. Our guide on how to clean a carpet cleaner hose walks through flushing and drying the hose, and our guide on how to clean a carpet cleaner brushroll covers removing hair and debris from the roller.
- Check the seals and gaskets on both tanks for cracks or wear, and replace any that are damaged. A worn seal is the most common cause of a carpet cleaner leaking during use.
Mistakes That Ruin Tanks
- Leaving dirty water in the tank. The number one cause of a smelly carpet cleaner. Empty it every time.
- Storing formula in the clean-water tank. Formula goes stale, leaves residue, and clogs nozzles. Mix only what you need for one session.
- Using bleach in the tank. Bleach damages seals and gaskets and can leave a residue that discolors carpet. Use dish soap and vinegar instead, unless your manual says otherwise.
- Putting a damp tank back on the machine with the cap on. Trapped moisture grows mold. Dry fully, cap off, before storage.
- Forgetting the float and filter screen. Hair wraps around the float and clogs the screen, which stops the machine from sucking properly and makes the tank overflow.
- Vacuuming up liquid with a dry vacuum. Liquids belong in a carpet cleaner or a wet-dry vacuum — see our guide on how to clean a wet-dry vacuum for the right tool and routine for liquid messes.
- Scrubbing with an abrasive pad. Scratches in the plastic trap dirt and bacteria. Use a soft bottle brush or cloth.
How Often to Clean Each Part
| Part | After Every Use | Monthly |
|---|---|---|
| Dirty-water tank | Empty, rinse, air-dry | Soap wash + vinegar rinse |
| Clean-water tank | Empty, rinse, air-dry | Soap wash, check formula cap |
| Tank cap and gasket | Rinse | Inspect for cracks |
| Float and filter screen | Rinse | Deep clean, check for hair |
| Hose | Flush with clean water | Full wash and dry |
| Brushroll | Remove hair and debris | Wash and inspect |
For the machine as a whole, the same storage logic applies as for any vacuum: dry, empty, and in a ventilated spot. Our guide on how to store a carpet cleaner covers draining the tanks, drying the hose, and keeping the machine ready between uses.
Products for Tank Cleaning and Care
The right formula and the right machine make tank care easier — a machine with removable tanks that lift out cleanly is far easier to maintain than one with a fixed tank you have to tip the whole machine to empty.
The BISSELL ProHeat 2X Revolution Pet Pro is a full-size carpet cleaner with a two-tank system that keeps clean water and formula separate from dirty water. Both tanks lift out for emptying and rinsing, and the machine’s heated cleaning helps lift ground-in dirt and pet messes. Use BISSELL formula in the clean-water tank and empty both tanks after every session.
The Hoover PowerDash Pet is a lightweight 12.5-pound carpet cleaner with a 0.5-gallon clean-water tank and HeatForce fast drying. Hoover rates it at 2X more cleaning power than the leading lightweight carpet cleaner. Its compact size makes the tanks quick to remove, rinse, and dry, which is exactly what you want for after-every-use maintenance.
The BISSELL Little Green 1400B is a 9.7-pound portable carpet and upholstery cleaner with a 48-ounce clean-water tank and a 1-year limited warranty. Its small tanks are the easiest to clean of any machine in this guide — they lift out, rinse in the sink, and dry on a dish rack in a few hours.
The BISSELL Deep Clean Pro 4X formula (78H63) is a 48-ounce concentrated carpet shampoo formulated to work in all BISSELL upright carpet cleaners. It is BISSELL’s most powerful formula for tough, ground-in dirt and stains. Mix only what you need for one session, and rinse the clean-water tank afterward so no formula residue is left to go stale.
The BISSELL PET PRO OXY Urine Eliminator with Febreze is a 48-ounce formula for use in leading upright carpet cleaners, designed for tough pet stains like vomit and mud. It is the best choice for the clean-water tank when the carpet has pet accidents, and it works with the same after-every-use tank routine: empty, rinse, dry.
Frequently Asked Questions
How often should I clean my carpet cleaner tank?
Empty and rinse both tanks after every use, and do a soap-and-vinegar deep clean once a month. The dirty-water tank should never sit full overnight.
Can I use bleach to clean a carpet cleaner tank?
Only if your manual specifically allows it. Bleach can damage seals and gaskets and leave a residue that discolors carpet. Warm water, dish soap, and a vinegar rinse handle almost every case safely.
Why does my carpet cleaner smell even after I empty the tank?
The smell is usually in the film on the tank walls, the cap gasket, the float, or the hose — not in the water you poured out. Wash the tank with soap, rinse with a vinegar solution, clean the hose, and dry everything fully with the cap off.
Can I leave water in the clean-water tank between uses?
No. Standing water goes stale and grows mildew, and leftover formula leaves a sticky residue that clogs spray nozzles. Empty the tank after every session and mix fresh formula next time.
How do I clean a tank I cannot remove?
If your machine has a fixed tank, fill it with warm soapy water, swirl, and use a wet-dry vacuum or a turkey baster to remove the water, then repeat with clean water. Dry it by leaving the cap off and running the machine’s suction for a minute with the tank empty. Most modern machines have removable tanks, so consider this when buying your next one.
My dirty-water tank has a white film. What is it?
It is usually dried soap and mineral deposits from hard water. A vinegar-and-water rinse dissolves it. If you have hard water, rinse the tank with distilled water for the final rinse to slow the buildup.
Final Verdict
Cleaning a carpet cleaner tank is a five-minute job that saves you from the two worst carpet-cleaner problems: a machine that smells and a machine that cleans with dirty water. Empty the dirty-water tank into the toilet after every use, rinse both tanks until the water runs clear, and let them air-dry with the caps off before you put the machine away. Do a soap-and-vinegar deep clean once a month, check the gaskets and the float, and never store formula or water in the tanks. A clean tank is the difference between a carpet cleaner that refreshes your home and one that makes it smell worse.