Sunday, October 2, 2022


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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7 months ago

Nanci, I think you’re making this harder than it needs to be. I have a Flush King that I attach to the sewer termination with a flush hose connected to it. I use my phone as a timer and let the water into the tank for 4 minutes based on the tank capacities. Very easy.

Bill Sax
7 months ago

We have had issues with our sensors not working correctly & mooch dock in our daughters driveway. Having accurate gauges would help plan the disconnect & trip to dump station 10 miles away. We have had the opportunity to have our tanks professionally cleaned and all the crud, solids, and icky stuff purged from both gray & black tanks has been unbelievable. Gauges work flawlessly now on our 13 year old motor home. Yes I have always done the tank rinse fill repeat. Traveled with soapy water in the tanks. But nothing has been as impressive as the professional cleaning.

7 months ago
Reply to  Bill Sax

Yes! The high pressure cleans and removes 95% of grey and black tanks. Once clean, three years excellent, very low maintenance required. Owner has since passed, sad , very intelligent man. He insisted that before traveling, tanks blasted, add pine sol. Not any copy cats! Been 4/5 years of clean sensors with nada, tank odors. I feel it’s time to repeat this maintenance. Truly makes poo… handling less stress for everyone.

7 months ago

We add simple vinegar to the black water tank before every trip. Never a smell problem.

john mack
1 year ago

My spouse and I traveled and camped in 48 states and it took us 9 years. Sadly, I wish it had taken longer. To my point! I read about the horror stories about the dreaded “BLACK TANK”. We never had a problem. What we did was this: Before we use the toilet we put several gallons of water in it and then the chemical. Every3 days or so we empty the tank. It is so simple and all I read are the terrible things that happen.
Just remember you are in a mobile residence and it does take a little more effort to maintain the RV.

2 years 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.

Bob P
1 year ago
Reply to  Hank

How do you know when to close the gray tank valve to prevent back flow from the black tank to the gray tank?

7 months ago
Reply to  Bob P

I just count to 15-20 & then close the grey tank valve, & re-open the main exit valve. I only use this method if we’re at a dump that doesn’t have a water source for flushing.

Ron Lane
7 months ago
Reply to  Bob P

It really depends on how your tanks are installed. Are they side by side and level with each other? If yes (as most are) the water level will equalize in each tank and prevent any back flow from the black tank to the gray.
I just wait until I don’t hear any further water noise traveling from gray to black. Simple.

2 years 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.

Bob P
1 year ago
Reply to  TIM

If you turn on the vent fan before perching on the throne then when you flush the vent fan will draw odors up from the tank. Endure the odors while on the throne, flush, then turn on the fan.

7 months ago
Reply to  Bob P

Or….turn off the fan before you flush.

Howard Jacobs
2 years 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…..

2 years 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.

2 years 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.

7 months ago
Reply to  Wayne

That’s about what I get even with a macerating toilet in the rear bath that takes more water than the 1/2 bath standard RV toilet. I get it with wasting water but water is your friend in sewage! I always dump when my tank is as full as I can get it so I have plenty of water to pull as much of the debris out as possible.

Deborah Mason
2 years 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.

2 years 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.

2 years 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.

2 years 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
2 years ago
Reply to  Denis


1 year ago

I agree. I can tell by the sound when I flush if tank dump time is close. Be aware and be happy.

Pam Scott
2 years 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.

Leonard Rempel
7 months ago
Reply to  Denis

Yup. I learned that after my first trip in the new RV. Tank sensors are useless, so just get over it. I also use a blade valve on the end of my discharge pipe and flush the black tank with the grey water. About 1/2 cup of Dawn in the tanks after flushing. Works better and vastly cheaper than the tank chemicals.

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