How to Clean an RV Black Tank
The short version: after you dump, run water through the black tank with the valve open, using the built-in flush inlet or a rinser wand, until the outlet runs clear. Then close the valve and add a few gallons of water and tank treatment. A clean tank comes mostly from habit: plenty of water, quick-dissolving paper, and keeping the valve closed until the tank is full.
What the black tank is
The black tank holds what goes down the toilet. The grey tank holds water from the sinks and shower. Each tank has its own valve, and both drain through the same outlet into your sewer hose. That's why you dump black first and grey second.
How to clean it, step by step
Empty the tank at a dump station
Dump the black tank first, then the grey tank, so the soapy grey water rinses the hose. Leave the black valve open.
Connect a dedicated rinse hose to the black tank flush
If your RV has a black tank flush inlet (a labeled hose connection on the outside wall), connect a hose you never use for drinking water. A backflow preventer on that hose keeps tank water from ever siphoning back into the supply.
Flush with the valve open until it runs clear
Turn the water on with the black valve open and watch the clear elbow at the outlet. When the water runs clear, you are done. Never leave the flush running with the valve closed and walk away: the tank can overfill and back up into the toilet.
No flush inlet? Use a tank rinser wand
A rotating wand goes in through the toilet and sprays the inside of the tank. Run it with the black valve open, moving it around, until the outlet runs clear.
Do a soak if the tank is stubborn
Close the valve, fill the tank about two-thirds with water and a dose of enzyme-based tank cleaner, and let it sit for a day, or drive with it so the water sloshes around. Then dump and flush again.
Close the valve and add starter water
Close the black valve and add a few gallons of water and a dose of tank treatment through the toilet. Solids should always land in water, never on a dry tank floor.
Habits that keep it clean
- Use a lot of water with every flush. Water carries the solids out when you dump.
- Keep the black valve closed until the tank is two-thirds to three-quarters full, even at a full-hookup site.
- Only RV- or septic-safe toilet paper. No wipes, even the ones labeled flushable.
- Add a dose of enzyme-based tank treatment and a few gallons of water after every dump.
- Never let the tank sit full for long, especially in hot weather.
If the tank won't drain
The usual cause is a pile of solids over the outlet, sometimes called a pyramid, from leaving the valve open at a hookup. Close the valve, fill the tank as full as you safely can with water and an enzyme cleaner, let it soak overnight, then dump. Repeat if you need to. If nothing drains at all, the valve itself may be stuck or broken, and that's a job for an RV service center.
Frequently asked questions
How often should I clean my RV black tank?
Flush it every time you dump if your RV has a flush inlet, and do a deeper soak or wand clean every few months, before storage, or whenever the sensors start reading wrong.
How often should I empty my RV black tank?
When it is about two-thirds to three-quarters full. For most RVers that is every 3 to 5 days, depending on tank size and how many people are aboard. Dumping a nearly empty tank leaves solids behind.
Should I leave the black tank valve open at a full-hookup site?
No. Keep the black valve closed until the tank is mostly full. With the valve open, liquids drain away and solids pile up on the tank floor. You can leave the grey valve open, but close it a day or two before you dump so you have grey water to rinse the hose.
Can I use bleach to clean my black tank?
It is best avoided. Strong chemicals can dry out valve seals and they kill the bacteria that enzyme treatments rely on. Use a cleaner made for RV holding tanks and follow the label.
Why do my black tank sensors say full when it is empty?
Waste and paper stuck to the probes inside the tank. A thorough flush, a wand rinse, or a soak with a tank cleaner usually fixes it.
What toilet paper is safe for an RV?
Any paper labeled RV- or septic-safe that breaks apart quickly in water. Use plenty of water with each flush.