Black Tank Flush, I’m puzzled

[Mogulite]

Just tried to flush my black water tank for the first time which should be a no-brainer. I’ve done it multiple times on my old rig.

So I attached the hose to the black tank flush, turn the water on, and nothing ! I left it on for a few minutes and nothing came out. So it appears that the water is being blocked somehow. Maybe a crimped hose.

I know it’s a stretch but has this ever happened to anyone else? It’s a 2019 coach, should be easy.

If I have to attempt to remedy this situation, is this a DYI situation?

[alank]

There’s a back flow valve right where you connect your hose in the coach. Take the hose off and gently poke around in there with a small screwdriver, the valve may be stuck.

[wingnut60]

New-to-you rig? In addition to a bad check valve, could be the nozzle in the tank is plugged. May need to remove and enlarge the holes.

[Mogulite]

Thanks for the suggestions. May not be a DIY job 🤔

[brandss]

My money is on what Wingnut suggested, a very common problem. Very easy to fix yourself. Typically on the passenger side the tanks are behind a panel that has 4 screws on each side. With the help of someone, remove the 4 screws and lower the panel. You will see the flush valve going into the top of the black tank, right in front of you. Remove the valve and take a drill bit and push out the gunk in each little hole. A lot of us use a drill and enlarge the holes a bit while pushing out the gunk. It is suggested that the holes are too small to begin with and the reason this is such a common problem. On a scale of 1 - 5, it's 1 with no special tools or skills needed.

[wingnut60]

Only thing I can add--when accessing the screws that hold the panel on (mostly hidden at the sides ) use protection on the screwdriver shaft so that you don't chip the paint on the panel edges. Not too hard a DIY, just patience getting the panel off--after that, everything is in front of you.

[BobGed]

While the attached photos are not for your particular coach they might give you an idea of what the previous posters are talking about.

The sprayer head holes should be drilled out to 3/32".

[gatorb8]

my backflow valve on the black tank flush was installed backwards from the factory. check that! easy fix

[wingnut60]

Don't you just love the QC nowadays...

[bneumann]

If you remove the panel to get at the tanks be careful not to strip the screws ... use hand not power tools & protect the edges (@ slit exposing the 4 screws) with 2 layers painter's tape.

You may also find the screws rusted out & possibly misaligned ... replace with strong stainless screws, hand tighten.

Support the panel when removing, it may have the manual water connection inlet on it with connecting plastic hose ... take more care than was done when first installed.

[Obrenn73]

Now I have a problem. When I go to flush my tank it seem I have a leak underneath my unit. I have look and trace the line and found that it goes into a penetration under the toilet. I can’t see where it goes from there. I have read that there is a vacuum plug on top to prevent back flow. Any suggestions is appreciated.

[alank]

If a line goes up under the stool, there’s most likely an identical line coming back down in the same place and going to the black tank. On top of those two lines will be a vacuum breaker valve. If they stick open they will leak when used. Mine was located under the 1/2 bath sink and I defeated the valve before it ever leaked under the sink. You’ll need to go to the stool area to find the valve.

[gdhugh]

Originally Posted by Mogulite

Thanks for the suggestions. May not be a DIY job 🤔

Simple

[Striider]

Originally Posted by gatorb8

my backflow valve on the black tank flush was installed backwards from the factory. check that! easy fix

Mine was backwards on my 2008 too, and it was in the wall of my shower accessed through the bedroom. My nozzles were also plugged. Here is my video about the fun:

https://www.youtube.com/watch?v=cTmDLbTvAUU&t=38s