Originally Posted by Flybob
You may have to pull the two sections of waste pipe apart. It looks like the seals are holding the valve in. Try gently pulling the dump connection away from the gate valve.
Yeah, I tried that. As I mentioned, I can't separate the pipes. The left side goes into an elbow and then up through the underbelly and won't move. The right side is on a hanger and then, past the Y, to another elbow and up to the grey tank. I've certainly tried to push them apart while pulling on the valve - there just isn't any play in the pipes.
Hmm, maybe I should try to slide a knife or something thin in between the valve and the flange.