Tuesday, March 21, 2023


Deep-clean the black tank to prevent nasty outhouse smell

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 black tank 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 to deep clean that black tank

Here’s a tip: Instead of using the popular wand device that always seems a little nasty after use and may whack against the flushers in the tank, I haul a hose with a sprayer attached through the window after flushing for a periodic deep clean of the black tank. 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 (personal protective equipment) 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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1 month ago

Closing one valve on a Y connection will keep anything from flowing back into your RV however without a back flow preventer it will allow the nasties to flow back into the campgrounds water system and potentially make everyone sick! Hopefully all of the black tank rinse systems have a back flow device incorporated with them as mine has, however just to be a Boy Scout I still use an external one.

Bob Weinfurt
1 month ago

I do this when I winterize my MH and have never had an odor problem with my black water tank.
I know there’s been a lot of debating and testing done over the ice cube cleaning method but I’ve found it to work very well. The issue I saw with most of the tests was they dumped in way too many ice cubes. Ideally, you want your tank a third to half full of water. To that I add a half teaspoon of Dawn and a five pound bag of ice cubes then immediately take it for a fifteen minute drive around the side streets of my town before draining. A few rinses later and the tank (and sensors) should be “crud” free and what remains of the ice cubes will help clean the drain pipe.
Why I said a half teaspoon of Dawn is just to help clean but more could lead to a foaming issue

Last edited 1 month ago by Bob Weinfurt
Capt. Jim
1 month ago
Reply to  Bob Weinfurt

Bob, I’ve been using and writing about this method for about 8 years on my Solitude. I use a bit more ice and a little less water. It’s a twenty min. drive to the free dump site at the marina. I try to use a little brisk braking to encourage sloshing. When finished, this is a good time to occasionally add a little valve lube.

Camper Jack - MyRVRadio
1 month ago

I use my phone’s timer feature. Without hesitation, when it goes off, I go dump. Middle of a conversation? Doesn’t matter. I generally will run the water, once initially emptied, anywhere from 7 to 12 minutes, depending on the water pressure. (We have very large holding tanks.) Been doing this over three years, never been an issue. But yes. Dump, rinse, empty, rinse, empty. Twice, when I can.

1 month ago

Counting to 200, using 1 second per beat, would be 3-1/3 minutes. I flush using my stopwatch for 5 minutes with the valve closed. Your manual should tell you how many gallons your black tank holds. Take a one gallon pail, run water into it until full and keep track of the time. Divide the time into 5 minutes and you’ll find out how many gallons you’ve added in that period. I would caution against trying to fill your tank for a good flush. The weight could damage the hangers, etc. Just do it partially a few times. Also remember your neighbors. When adding water to a black tank when the valve is closed pushes any smell up and out the roof vent so anyone down wind gets to enjoy the fragrance.

1 month ago

“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.”

I’m having a hard time imagining what you are describing. There should NEVER be any kind of “connection” between a sewer flush system and your freshwater system. In addition, the sewer flush system should have a backflow preventer built in. Perhaps I’m misunderstanding the setup.

Jim Johnson
1 month ago

Consider an anti-siphon valve and a water flow meter for your flush hose. The meter goes on the tap first, then the anti-siphon valve, and finally your flush hose.

While your black tank flush system should already have a factory installed vacuum break, the anti-siphon valve will prevent potential contaminants from getting to your potable water source. Belt and suspenders approach.

Many of us close our black tank waste gate to partially refill our black tank for a better flush. Originally I guestimated the volume of water (gallons per minute) and used my watch to time it. Nancy does about the same by counting. We all know campground water systems are anything but consistent, so you are overly cautious – or should be. But with a flow meter, you will know how much water you are putting into your black tank.

I use the second flow meter to determine how much fresh water I am putting into our internal tank.

1 month ago
Reply to  Jim Johnson

That little meter is a great addition to an RVers gadget kit!

Camper Jack - MyRVRadio
1 month ago
Reply to  Jim Johnson

The flow meter would only be effective once you’ve dumped. As we all know, blank tank sensors simply don’t work after a time. And with our rig, I’ve never been able to find the numbers for the size of the *front* black tank, separately from the rear black tank. Heh.

John Goodell
1 month ago

I also rinse thoroughly by alternating the valve closed and open. I started out ‘guesstimating’ a few minutes for the flush, but there are too many distractions and I was worried that I would eventually have a catastrophe. I started using the timer on my phone or watch which worked pretty well. The best method, in my opinion, is to use a flow meter (Orbit 56854 Hose End Water Flow Meter). It is accurate and allows me to confidently add 10 or 20 gallons for a rinse and then 5 gallons when I was done.

Neal Davis
1 month ago

Thanks, Nanci! Rinsing is very important. I don’t think that we ever got the black tank on our first RV completely clean. I always wanted to go to Florida or Arizona and have it professionally cleaned (as the RV Geeks showed in one of their videos). Sadly, we traded before ever reaching the service area of such a company. Hopefully RV #2 will get better treatment.

1 month ago

I use to sit from end of April until mid October. We always used lots of water when flushing and I would dump every Sunday. I had a built in flusher so I would run water for 10 minutes then open the valve and dump allowing the water to run. When it was empty I close the valve and run 5 minutes of water into the tank so that there was water already in the tank. This was a 50 gallon tank.

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