A black tank treatment controls odor and helps break down waste and toilet paper. It cannot clear a pile of solids sitting under the toilet; that takes water, time and flushing. Dose it by the bottle after each dump, and rinse the tank with its own hose.
RV Black Tank Treatments and Cleaning: What They Do and the Clog They Cannot Fix
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At a glance
- What it does: deodorizes and breaks down waste and tissue, as the makers describe it, but does not dissolve a solid build-up.
- Typical dose: 2 to 8 oz depending on the product, or one drop-in packet, per 40-gallon tank, added after every dump.
- No bleach: Thetford and Dometic both say bleach and harsh chemicals can damage the toilet seals.
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What a tank treatment actually does
A treatment is routine upkeep against smell and sticking waste, not a repair. Thetford says Aqua-Kem Liquid liquefies waste, breaks down tissue to prevent clogging, cleans the tank walls and drain lines, and deodorizes the tank. Enzyme products work differently: they speed up the natural breakdown of waste and toilet paper.
Results vary by brand, so Keystone says to try a different one before suspecting the plumbing. Treatments also need liquid to work: Walex says to add about 1.25 gallons of water for every 10 gallons of tank capacity, the same reason the black tank drains solids better when it is fairly full.
Types of treatment and how much to use
Any type made for RV holding tanks will do the job if you dose it by the label; there is no ranking here.
| Type | What the maker says it does | Dose |
|---|---|---|
| Chemical deodorant (Thetford Aqua-Kem Liquid) | Liquefies waste, breaks down tissue, detergents clean tank walls and drain lines | 8 oz per 40 gal |
| Enzyme (Thetford Aqua MAX, Campa-Fresh) | Deodorant and waste digester, formaldehyde- and bronopol-free | Per the bottle |
| Bacteria and enzyme (Camco Rhino Enzyme) | Digests waste, tissue, fats and proteins | 2 oz per 40 gal |
| Drop-in packet (Camco TST, Walex Porta-Pak) | Breaks down waste and tissue, odor control up to 7 days | One packet per 40 gal tank |
Doses from Thetford's product pages, the Camco RV accessories catalog and Walex's product pages.
Tip: The US EPA's alert for RV owners warns that some odor-control products contain chemicals that may pollute water or corrode a septic system, and names formaldehyde among them. Formaldehyde-free versions say so on the label: Thetford AQUAbio, Aqua MAX and Campa-Fresh, Camco's TST line and Walex Porta-Pak.
How to flush and clean the black tank
A flush after the dump rinses out what the treatment loosened. If your RV has a black tank flush inlet, the hose feeds a sprayer inside the tank. Jayco's 2027 towable manual gives the sequence:
- Dump the black tank and leave the black tank drain valve open.
- Connect a garden hose from the water source to the black tank flush inlet.
- Turn the water on and flush until the water running out of the drain valve is clear, not discolored or cloudy.
- Turn off the water, disconnect the hose and close the drain valve.
Jayco says the drain valve must be open any time a hose is connected to the flush inlet, and no hose stays connected when you are not flushing. Airstream allows a rinse with the valve closed, but only for a couple of minutes so the tank does not overfill.
No built-in flush? Forest River says to rinse through the toilet with several gallons, closing the toilet valve so the bowl fills and releases with more force. A flush wand such as Camco's Swivel Stik dislodges deposits left on the walls after the tank is emptied, and Camco's Blaster rinsers attach at the sewer discharge pipe instead.
Tip: Keep a hose only for flushing. Camco sells its grey and black water hose in bright orange so it is not mixed up with a drinking water hose. A rinser with a built-in backflow preventer stops sewage siphoning back into the water supply.
Can I use bleach or household cleaners?
Keep bleach and harsh cleaners out of the system, because they damage the toilet seals. Thetford says bleach and the acids in most household cleaning products can dry out the seals, and it also rules out petroleum-based products, scouring powders and concentrated cleaners. Dometic's 400 series manual says the same of chlorine, laundry bleach and drain-opening products. Winnebago's simpler rule: no chemical additive that is not approved for RV use.
If freezing is a risk, Thetford says to use RV antifreeze in both the black and grey tanks, never the automotive kind. A damaged seal shows up later as a bowl that will not hold water, one of the more common RV toilet problems.
The clog a treatment cannot fix
A pile of solids under the toilet needs water and time, not more treatment. Thetford says it forms when the black dump valve stays open during use, even on a full hookup: the liquid drains away and the solids build up directly under the toilet until they plug the toilet and the whole tank. Airstream says too little flush water does the same. Keep the valve closed until the tank is at least three-quarters full.
Keystone's 2027 manual gives the fix: close the valves, fill the tank about three-quarters full with fresh water, drive a distance to agitate the solids, then drain. If that fails, a waste water digester from a dealer may help. For a paper clog, Thetford's Tissue Digester is sold to break down tissue, and toilet paper made for RVs prevents the next one.
A sensor stuck on full
A full reading right after a clean dump usually means residue on the probes, and a soak product clears it:
- Camco Rhino Holding Tank Cleaner Drop-INs: one per 40 gallons of capacity, tank filled three-quarters with water, works in under 24 hours; Camco suggests one every three months.
- Walex Commando: one packet treats up to 50 gallons; fill the tank so the water covers all the sensors and let it sit 12 to 24 hours.
- Thetford Level Gauge Cleaner: half a bottle into a 40-gallon black tank through the toilet on a warm day above 75°F (24°C), mixed by driving, left 24 hours, then emptied and rinsed. Not for the fresh water tank.
Keystone also recommends filling the tank with fresh water now and then and dumping again, which keeps the monitor panel reading correctly.
Common questions
Can I put bleach in my RV black tank?
No. Keystone's 2027 manual lists detergents and bleach among the things that must not go in the toilet or drains, alongside automotive antifreeze, ammonia, alcohols and acetones.
Can I use dish soap or household cleaners in the black tank?
Jayco says not to add caustic chemicals such as laundry detergents: they may deodorize, but they can damage the plastic and rubber parts of the plumbing. If you want a cleaner, Thetford notes that mild organic acids and citric acid will not harm the seals.
How often should I flush the black tank?
Jayco says each time the tanks are dumped, or as needed. Forest River suggests a deeper clean after every third emptying, filling and flushing both tanks with clean fresh water a couple of times.
How often should I add tank treatment?
After every dump, in the amount the bottle specifies; Winnebago has you add water and treatment before traveling so the tank is treated on the road. Dometic's older 510 manual notes that very warm weather, longer holding times and larger tanks may call for more.