By Nanci Dixon
Who knew I could get so excited about flushing the gray and black water tanks? Okay, I know it is a bit odd, but as the designated tank flusher I am happy when the “gunk” comes out. While I am diligent about flushing out the black water with the built-in flush system, there was no built-in system for the gray water. When I complained to our RV tech about the smell when driving, he said that the gray water can smell worse than the black.
Why?
Mold in the gray water tank
I recently attended a rally seminar about “All things black and gray” and, boy, did I learn a lot! The presenter from Kleen Tank passed around glass bottles of “stuff” that had come out of holding tanks. He did advise, “Don’t open, don’t drop,” while handing it off.
I recognized the black discs that had been coming out of the gray water holding tank and was disgusted when he said it was a massive amount of mold. He also had some discs as hard as metal that he passed around that had “mineralized” with the urine in the black tanks. He said that he finds the gray tank is usually worse than the black, particularly if people have built-in flush systems and had been keeping up with the black tank.
Flush rinser with gate valve and water meter
Best of all, he passed around this flush attachment and water meter. I knew the flush rinser existed, but our hose goes straight down through the bay and there was no way the flush attachment was going to fit. But wait! He showed how the gray and black dump pipe rotates outward and allows the flush rinser to attach! This is what he showed me.
Combined with a water meter, the flush rinser can easily clean out both gray and black water tanks.
The water meter measures how much water is going through a garden hose. It is usually used when watering a garden but it is an exceptional tool for measuring how much water in gallons or liters is going into RV tanks, particularly when flushing. (You can read more about this handy water meter here.)
Warning and Disclaimer:
THE FOLLOWING METHOD IS GENERALLY NOT RECOMMENDED BY RV MANUFACTURERS.
It is not recommended because there can be disastrous results if one walks away from the RV or gets distracted while filling a closed gray water tank or closed black tank with water. Think black water eruption through the toilet into the bathroom and beyond…
With that disclaimer noted, this was the method taught at the seminar to thoroughly flush out the black water and gray water tanks. This was also the method Kleen Tank used when flushing out our tanks. They had the additional step of a hose inserted into the tanks to pressure wash them along with flushing them out. That pressure wash is what a professional is for!
Flush steps
1. IMPORTANT! Double-check the gallon capacity of the holding tanks in the RV specs. If you are like me, it is a good idea to write them down!
2. Attach water meter to a garden hose. Do NOT ever use a fresh water hose to flush! Use a backflow preventer to prevent contaminated water going into fresh water faucet. Kleen Tank adds the backflow preventer and water meter at the flush rinser. Others put the preventer and meter at the faucet.
3. Attach the flush valve rinser to the sewer pipe opening and sewer hose.
4. Pull gray water valve open for a few seconds and close to “lubricate” the sewer hose.
5. Dump black water.
6. When black tank is empty, follow directions on the flush valve rinser, close the rinser gate valve and fill the tank with water.
7. Watching the water meter, fill UNDER the capacity of the tank. I went under by 20 gallons just to be safe.
8. Turn off water and pull gate valve. If you can stand to watch, see how much more gunk was in there.
9. Repeat with the gray water tank. If your tank was like ours, it was not a pretty sight!
10. This flush rinser has a hose rinse setting, too, but I found it rather ineffective and figured the gray water going through the sewer hose was rinse enough.
11. Add at least two gallons of water to the black tank through the toilet and then treat as normal. A number of people are so happy with this type of flush they don’t add any chemicals, organic or otherwise, to the tanks.
And that’s what you call a royal flush! Happy flushing!
RELATED
- Tips to clean a gunky gray water tank. Yes, yours is gunky too
- Understanding your RV’s sewage system: Proper black and gray tank upkeep and maintenance
- My RV’s gray tank valve handle and rod are missing. How can I drain the smelly tank?
- How to deal with gray water tank odor in your RV
RVDT2938
These back flushers feel like a gimmick to me.
Filling a tank from the bottom up with the weight of the water increasing on top suggests any possible “scrubbing” action will be less effective than merely dumping five gallon buckets of hot water down the shower or taking a longer shower….
Better yet, close the valve and let water accumulate between dumps and even better yet, let that accumulation slosh between hookups.
I think grey tanks stink because folks leave the grey valve open when they’re connected and don’t understand removing solid sink debris that goes into the tank from dishes needs almost the same high volume “whoosh” the blank tank does.
I have to agree with you. Putting water into the dump valve is basically trying to push it uphill. The initial blast may clean the pipe, but once the tank starts to fill, there is no longer any force to cause the water to agitate inside the tank. It just fills the tank.
Can someone please explain like I’m 5? If I have a separate hose for the flush, why do I need a backflow preventer?
Also, if we sanitize our fresh water tank with a bleach solution, and see no chunks flowing out, can we still have mold?
I’ll give it a stab Cookie:
Think of someone with a canker sore who backwashes using your straw to drink from your cup.
With that visual in mind, consider how some of the black tank contents can come out of the flush tube once the water is turned off (since pressure holding that “stuff” out of the hose drops off) so the question is where do we want whatever comes out to go.
Do we prefer that stuff dribble out of a backflow preventer at the flush fill elbow connection or is it worth the risk of it dribbling down the length of the hose we attached to the elbow and adding stink to the flushing hose.
On our 2017 Cougar the flush line just dropped water into the tank. You can do the same using the toilet, but you cannot easily judge the amount of water going into the tank. Gail says use the meter to add less than a full tank of water. Smart. But also know that to ‘float’ ‘stuff’ off the sensors you have to get at least that full. About every 6 weeks I would resort to turning off water to the toilet (what, you don’t have a shut-off?, get one) using my Camco flex wand to spray off the sensors. For gray tank, periodically used Thetford Tank Blaster.
Thank you for the discussion and instructions, Nanci. This is all interesting and helpful. Have a great day and safe travels!
On our little travel trailer, the belly isn’t enclosed and I had access to the tank. I installed Camco’s Tornado Tank Rinser. Does an excellent job of cleaning the black tank. If the gray gives me problems I will install a second unit there. Recently upgraded the toilet and got a good look at the black tank – not sterile but very clean.
Hint. I installed the Tornado at the high end and substituted a garden hose for Camco’s vinyl hose and routed the input to the other side near my waste gates with a quick connect.
This is a must have to keep gray tank clean. It works and keeps my sensors reading empty all the time.