Black Tank Flush

Ok, I know this will look "familiar", (as in Fresh Water Tank Fills by Itself), but it's not the same (I don't think).

While I was docked and preparing to depart an RV park, I was dumping the tanks. Black tank first; I hooked up a hose to the flushing fitting in the UDC, turned the water on and opened the gate valve. So far so good. I turned the water off to see when the tank was actually empty (via clear elbow on sewer hose). Then I closed the gate valve and turned the water on again. About the third time I did this, I heard water dribbling and then saw my fresh water tank overflow was spilling. Huh???

I checked this file: Water Systems Guide V1.1.pdf to see a water system diagram (pg. 6). I see NO connection between the flush line and the fresh water tank.

Any ideas???

There should be no connection from black tank flush to the fresh tank at all. Due to sanitary reasons of course. Are sure you had the hose hooked to the correct input??

PondSkum said:

There should be no connection from black tank flush to the fresh tank at all. Due to sanitary reasons of course. Are sure you had the hose hooked to the correct input??

Click to expand...

Yes, I am sure, see photo.

My black tank flush put water in the interior of my pioneer and was also running it out from the sealed portion of the TT today. Still mystified as to what has happened.

Sent from my SAMSUNG-SM-G935A using Tapatalk

Gadgetman said:

Yes, I am sure, see photo.

Click to expand...

OK, you need to get into the crawlspace behind the UDC and TRACE where the tank rinser hose goes. This sounds like a misconnected tubing. It SHOULD go to the black tank under the toilet. The freshwater tank is near the spare tire mount in the rear on my rig. Normally your tank fill tubing (on newer rigs) comes off of the 4 way valve (See: https://manuals.heartlandowners.org...erson/Anderson Valve Detailed Explanation.pdf ) . The black tank flusher is a seperate line - See the plumbing for it here: https://manuals.heartlandowners.org/manuals/Plumbing/Tanks/Black Tank Flusher2_Install_.pdf

Is it possible that the water was not coming from the tank but was just flowing out around the overflow drain? Quite possible that the flush line’s anti-siphon valve is broken and is dumping water into the underbelly. That is not an uncommon failure and is NOT necessarily due to high water pressure.

Mine failed a couple of seasons agoand dumped water into the kitchen. All water entering my rig goes through a Watts regulator and the pressure gauge has never read more than 45 psi. Cheap plastic, poorly molded, is the cause.


Sent from my iPhone using Tapatalk

I agree with John that the anti-siphon may have failed. Mine has never worked from day one. However, the failure may have occured from "high" pressure too. A lot of folks do not use the pressure regulator when flushing the black tank but probably should.

The water feed for the black tank, on my last two rigs, was the braided(see photo) white hose, not PEX. I totally agree with the failure of the ASV, causing the water in the under belly routine. Mine failed on both of my last two fivers, so I eliminated that and its plumbing.

JohnDar said:

Is it possible that the water was not coming from the tank but was just flowing out around the overflow drain? Quite possible that the flush line’s anti-siphon valve is broken and is dumping water into the underbelly. That is not an uncommon failure and is NOT necessarily due to high water pressure.

Mine failed a couple of seasons agoand dumped water into the kitchen. All water entering my rig goes through a Watts regulator and the pressure gauge has never read more than 45 psi. Cheap plastic, poorly molded, is the cause.


Sent from my iPhone using Tapatalk

Click to expand...

No extra water anywhere (or spilled, etc.) Thanks for the thought though!

wdk450 said:

OK, you need to get into the crawlspace behind the UDC and TRACE where the tank rinser hose goes. This sounds like a misconnected tubing. It SHOULD go to the black tank under the toilet. The freshwater tank is near the spare tire mount in the rear on my rig. Normally your tank fill tubing (on newer rigs) comes off of the 4 way valve (See: https://manuals.heartlandowners.org...erson/Anderson Valve Detailed Explanation.pdf ) . The black tank flusher is a seperate line - See the plumbing for it here: https://manuals.heartlandowners.org/manuals/Plumbing/Tanks/Black Tank Flusher2_Install_.pdf

Click to expand...

Thanks for the suggestion!

I got behind the UDC and traced pipes. The Tank Flush fitting/blue pipe goes up behind the shower panel to the ASV. Coming out of the ASV is red pipe, but once it exits the floor (into the cargo bay next to the UDC), it changes to white reinforced flex line that then disappears below the cargo bay floor heading down towards the tank. So, I can see no connection to fresh water tank. Someone suggested what I saw was coming from the underbelly, but it was definitely coming from the fresh water overflow tube. So, I am at a loss for what actually happened. Once I got home, I tried to duplicate it; made sure the fresh tank was full, hooked up regulator and hose to Black Tank Flush connection and turned the water on. Let it run for 5 minutes and observed NO water overflow from the fresh water tank.

So, I am wondering IF coincidentally while flushing the tank, that the check valve (or backflow valve) on my water pump went bad and filled the tank because I was still hooked up to shore water at the time I observed the overflow condition at the RV park while flushing the black tank.

Ahh, possible that the Anderson valve is allowing water to go to the tank, even though you have it set not to. Been enough reports of them leaking internally and eventually overflowing the fresh water tank.


Sent from my iPhone using Tapatalk

JohnDar said:

Ahh, possible that the Anderson valve is allowing water to go to the tank, even though you have it set not to. Been enough reports of them leaking internally and eventually overflowing the fresh water tank.


Sent from my iPhone using Tapatalk

Click to expand...

Thanks! I was just reading up on that, and think that may be the problem!