Tank Flush No flow

[ColinB-KEY]

First time using the flush, actually getting ready for the weekend and thought I’d use the flush connection to add 2 gal to black tank with the ol’ toilet tab. Heard good method on the way to the site for the blue water to slosh around on the way. Connected my hose and NO flow. Removed the hose and back pressure spray. Going back out to look in the pump bay to see if there’s a check valve backward.

 

[chuckster57]

The check valve is most likely in the cabinet under the bathroom sink. If not there then it may be behind the shower wall.

 

[NH_Bulldog]

It does sound like a check valve issue, as they can be installed backwards.

Another thing to consider is age of the trailer and how many times the black tank has been used without engaging the flush. It is very easy for “debris” to clog the tiny holes in the spray head and then dry and turn to cement. If that is the case, there is almost no coming back from that. At least the valve is any easy fix so I am keeping my fingers crossed for you!

 

[jxnbbl]

The third thing to consider is what happened in our case with our first trailer (new). The pex piping had been 'folded'. What had to be done to correct this was to cut the fold out of the pipe and put in some "one straight" connector like an elbow to allow bending....of course to do this access is a problem. Hopefully the normal check value problem is the case!

 

[ColinB-KEY]

Thanks for your comments, so here it is. Photos attached. Doesn’t look to be installed backwards. Saw other posts this site to just remove and splice. What in tar nation dad burn it is this doing up there? So if it’s backwards, swap the connections of the two white tubings.

 

[Stumpy75]

Thanks for your comments, so here it is. Photos attached. Doesn’t look to be installed backwards.

Somewhere on that back check valve, there will be an arrow for direction of flow. Probably on the side that's impossible to see. Mine just quit working and would not allow any flow at all. I got an inline Sharkbite back check valve for mine...

Another thing to consider though is that the sprayer itself might be plugged. If the back flush has not been used in a while, the poo will harden in the sprayer...

 

[chuckster57]

You need to verify that the “in” pex is actually the “IN” pex. If you have a helper, take the line off and use compressed air at about 20 PSI.

 

[ColinB-KEY]

Thanks for the input. Went ahead a bought a new one just in case. First plan is to remove and check inlet tubing with air. Then pipe in elbow to check if nozzles are plugged. This RV is 3 months in use, but 18 months old. Bought a 2024 in Dec. Likely not plugged, but will check with water. I like the idea of just a check valve just on the other side of the connection in the pump well.

 

[ColinB-KEY]

Case closed! Finally had some time to work on it. Removed widget, used 20 PSI air to identify inlet. Backwards. Labeled, reinstalled, bingo. She’s a gusher. Thanks all for the ideas.

 

[wingsfanromeo]

Case closed! Finally had some time to work on it. Removed widget, used 20 PSI air to identify inlet. Backwards. Labeled, reinstalled, bingo. She’s a gusher. Thanks all for the ideas.

I have the same issue with my 2025 Outback 328RL. I tried using it for the first time and no water was going in. my check valve is under the bathroom sink and the white hoses aren't labeled to tell you what is the incoming water and the outgoing one. since it's new and under warranty I have it at General RV so they can fix it. I'm thinking that is probably the issue though just like yours.

 

[chuckster57]

Checking the function of the black tank rinser should be a normal part of the pre delivery inspection done by the dealer, and the inspection form filed with the manufacturer.

I’ve seen warranty claims denied, because the issue was signed off by a tech as “good” on the PDI sheet. So it’s not just a dealership issue, but also an employee issue.

Having spent 25+ yrs in law enforcement, I learned real early, if your name is on it, it better be correct.

 

[Sonders]

We spent 2 weeks traveling a few months a go, and never hand a chance to use the flush valve when dumping. I attempted to give ours a thorough flushing once we got home, but it was too late; it had no flow. I removed the check valve when first bought the rig and replaced with a pvc elbow so I know that's not my issue. To trouble shoot I ran water from the water bay (which is in very front) back to the under bathroom sink connection where the check valve used to be. I simply unhooked it and placed a bucket to catch the water as it ran. I had water coming back that far, but wasn't getting into the tank, so determined it's the sprayer nozzle that is clogged. Not a fan of the black tank flush being up front in water bay, when black tank is all the way in the back. That is a very long distance for water to travel to even reach tank. I'm going to change the nozzle out sometime, and reroute a new flush connection back near the dump valves for quick and easy access and a whole lot less pex line.

 

[JRTJH]

Has the spray nozzle ever worked ???? Your first sentence sort of suggest that you've never used the flush valve when dumping. There are some instances where the PEX tubing from the vanity down to the black tank is "bent too much" and actually shuts off waterflow. So, before "chasing down the nozzle inside the tank" if the system has never been verified to be functionally operational, then I'd look at the PEX before ripping into the black tank. Remember that even in the "dry desert" it takes significantly longer than a couple of weeks of "non-use" to completely dry out the solids in the black tank. If you were using the toilet on that trip, I would almost guarantee that there's nothing "dried on the nozzle preventing waterflow" that occurred in a two week period. If you've never used the system before and are unsure if it ever worked, check the PEX before getting into the really disgusting parts ...

 

[Sonders]

Yes, it worked fine before the trip, that’s what was super frustrating. I have plenty of water pressure all the way to the backflow valve; it’s just not getting to the tank from there in that short run under the sink. I went as far as hooking up air compressor on the end of pex line going down into the tank and letting the air pressure blow through the nozzle. I have the black tank about halfway filled with water so I can see how much air is flowing through. It seemed to work before our weekend trip a few weeks ago, but when we got home and I tried running the flush again; back to no flow.

 

[wingsfanromeo]

I have the same issue with my 2025 Outback 328RL. I tried using it for the first time and no water was going in. my check valve is under the bathroom sink and the white hoses aren't labeled to tell you what is the incoming water and the outgoing one. since it's new and under warranty I have it at General RV so they can fix it. I'm thinking that is probably the issue though just like yours.

update to my black tank flush issue, it was indeed the same thing where the check valve was installed backward. General RV did a bunch of troubleshooting to include looking at the hoses and black tank then checked the valve and found out that it was connected backward. no cost to me thankfully since it was all under warranty.