[Motor31]

Sewer dump valves are pretty common in RV supply stores, both the 3" black and the 2" grey variety. I would recommend setting up the pipe with a standard valve assembly so that later on when the valve goes bad you can replace it just like the ones currently installed in the rig. They are bolt on sections rather than glue on. If you use a strictly glue on you will have to cut the pipe again to do the replacement. Eventually you'll run out of extra pipe.

Who ever decided to put the pipe in the wheel well as well as other stuff really should look at the situation and see how it relates to the tires in the real world. It's a lot different on the road than it is in the showroom. IMO it's hardly a case of good thinking in the design.

FWIW I have already had a failure of the black tank valve assembly. Of course it was with a full tank. I had to get to an RV service center and they opened the valve manually to dump it. Then replaced the valve with a standard "T" handle valve. A replacement cable valve was not available at the time. I now reach in the basement to open the black tank as the cable pull as installed by the factory was very hard to move. Lubing it wasn't helpful and that led to the failure. When I pulled the cable I had to use both hands.

The grey valve isn't nearly as accessible and I am dreading it's failure. I am afraid that I will be stuck installing another cable pull when that happens.