Black Tank Flush Issues

[Madmax07]

Last fall when we were finishing up our last trip, I was packing up and went to do a black tank flush. I hooked up the hose to the black tank flush at the convenience center. The hose pressurized but water wouldn't enter the black tank.
Suspecting a problem with the crappy plastic check valve, I removed it and joined the 2 lines together, with the intent of installing a check valve at the black tank flush inlet.

I turned the water on and again the hose pressurized. I was under the sink because I was worried about possible leaks where I joined the lines together. I did have a slow drip from one of the connections.

However, that wasn't the biggest problem. Water was still not going into the black tank. At this point I'm not sure what to do. Obviously, water is getting to the point where I connected the lines, but there must be a problem further along. Is dropping the underbelly and black tank my only recourse to figure out what's going on?

[Daryles]

Dropping the coroplast on the forward drop down is easy. Use a drill in reverse with a 1/4" socket on the nail head. Pry down under the fender washer. The nails will come right out. Since you are after the flush system, tank down the front edge first. Take down only what you need to work on it, or take it all down. I had to replace the black tank valve seals. I added insulation while I had it open.
To put it back up secure the forward edge first then work your way back. Use 2x4 (pole) on leveling blocks to hold it up as you secure it. Use 1" #12 self drilling bolts through the nail holes. These will go through the frame without holes but you have to push HARD.
Follow the white pex pipe forward. You will find the flush device at the front of the tank.

[Madmax07]

Thanks for the detailed information. I would struggle to do this without it. Where exactly are the valve seals located?

[DutchmenSport]

To solve your problem immediately, until you can find a fix, you can always grab a black tank toilet wand and connect it to a garden hose and shove it down the toilet and spray out your black tank. Actually, it's a good idea to keep one of these as part of your RV maintenance arsenal. One advantage of the toilet wand is the fact, it will spray out the neck of your toilet where a lot of stuff clings.

Now, if your camper has a curved drop from the stool to the tank, then the wand won't work.

[Daryles]

Originally Posted by Madmax07

Thanks for the detailed information. I would struggle to do this without it. Where exactly are the valve seals located?

The black and Grey 1 (shower/sink) dump valves are just forward of the rear edge of the front drop down.