Deep-clean the black tank to prevent nasty outhouse smell


By Nanci Dixon
When the winds of time blow in the wrong direction and the bathroom vent just doesn’t seem to siphon all the scent away, it is time for the deep clean. Sigh. We have a flush system that works pretty well. Dump, rinse, repeat, rinse, repeat. I will admit that I do close the tank, fill with water, count to 200 and dump again – against every warning plastered in our water bay.

Having read horror stories about where the black tank flush can go with the valve closed, I do not move from the water bay. I keep my feet firmly planted next to the valve. I used to try to count to 200 in Spanish so I would stay focused and not wander off or talk to anyone but could only remember enough to get to 80. Back to English I go.

Prevent contamination

We have a two-hose valve setup with a blue flush hose on one side and a white fresh water hose on the other side. It is important to turn off the fresh water to the motorhome while flushing to prevent any flush water from contaminating the fresh water system. You do not want that to happen.

Use a hose

Here’s a tip: Instead of using the popular wand device that always seems a little nasty after use and may wack against the flushers in the tank, I haul a hose with a sprayer attached through the window after flushing for a periodic deep clean. I use it to adequately rinse off (actually blast off) the, ummm, “crud” on the pipe going to the black tank, with the black tank valve OPEN.

Avoid splashback… yuck

The hose works well BUT (and this is a big BUT) there can be some splashback if the hose doesn’t fit perfectly. And that really is nasty. If that happens, a shower and vigorous hair washing are required. Here is where PPE comes in handy. I saw an opportunity when our local CVS started carrying face shields.

Now, with my gloves on and my face shield in place, I can spray off the pipes. I do double-check with a flashlight to see the progress and once again wonder why those pipes are white instead of black.

If this doesn’t help with your stinky RV bathroom, well, good luck…


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21 days ago

I think filling your black tank 2 or 3 times is a huge waste of fresh water. And fresh water is coming harder and harder to get. And I am not a water nut. And not a waster. For over 13; years, I have let my gray float into my black (after I have emptied the black) about 3 times. By the third time it is usually clear coming out. Then I let a little more gray in the black, so it is NEVER DRY. then close the black tank and finishing dumping my gray, thereby washing out my hose. No need you’re up all that fresh water. We are going to need it someday! It is getting pretty expensive now. And that is why your RV park fees aren’t going up folks! 40 to 60 gallons of freash water every time you dump, plus what was in you tanks. And all that water goes into a sewer system somewhere to be treated, and that’s not cheap! Check you home water and sewer bill. You will understand.

24 days ago

Black tank obsession is bizarre and most of those afflicted are going about it all wrong. If you get odor anytime other than the brief instant the toilet is flushed, you have a plumbing problem that needs fixed. A correctly installed system has no odor inside the RV. Stop the black tank religious fervor and fix your plumbing.

Howard Jacobs
25 days ago

Tip for rinsing the black water tank. I bought a digital counter for the water hose. I have a 40 gallon take and put 30 gallons in the tank before I empty. Two cycles and the water from the tank runs clear. Take care and stay safe…..

26 days ago


Here are my ideas:

Use the clock on your phone rather than counting.
Use a Flush King rather than snaking a hose through the window.
Get a blade valve and connect it to your sewer outlet. Leave it closed but open both the black and grey valves to let the tank equalize. You’ll get more capacity for gray.

26 days ago

4 or 5 days!! Yikes. Boondocking last winter in the desert we managed to go 14 days before needing to dump the black tank. And no…I did not make her go outside.

Deborah Mason
26 days ago

When we spent the summer of 2015 living in our MH while taking care of my MIL, we found the black tank filled in 4 days. Having to put everything away, drive 5 miles to dump, 5 miles back, set up, only to have to do it again 5 days later got old. We tried putting the paper in a waste basket (emptied daily). 10 days between trips. Bonus? Our black tank sensors work better without paper. Win-win.

26 days ago

I put water softener, the black tank chemical and some powdered laundry detergent in my black tank. Whenever I dump it, I first fill it to the brim using my Johnny Chock. After I dump the black, I close black valve and dump my grey. Seems to work quite well.

26 days ago
Reply to  John

And a key ingredient is time. Even if I can’t find Calgon and don’t have a tank rinse system, I can at least flush the tank, fill with clean water, and let it sit for a few hours or even overnight, dump again.

I think people who have persistent buildup problems may have a bad tank design (angled drop into the tank etc) that creates the problem, and for them I guess more aggressive work is necessary.

26 days ago

Why does everyone wants the black water tank as clean as a fresh water tank?
Learn to live with sensors that are useless, learn how long you can go before the black water tanks is full and use a lot of water to flush when possible.
Just saying.

BILLY Bob Thronton
26 days ago
Reply to  Denis


Pam Scott
26 days ago
Reply to  Denis

I totally agree. We clean the tank when it is dumped. Sensor shows zero. Soon it rises to 33-67%. We do not trust it. But, we can usually go at least four days at a minimum for two people.