Making a couple of plumbing repairs to my 19 year old Class A. One of them was my black water knife valve was leaking, not serious, but when you removed the drain cap a bunch of stinky brown water would come out and run all over everything. So I went to the RV parts store and got a replacement seal kit. So this morning I take apart the valve. Now this is a system where the gray water tank and the black water tank share a common discharge, using a molded plastic assembly that has a knife valve at each end. I removed all the screws for the black water valve, but couldn't get it out of the piping. It seems that the seals extend into the ends of the adjacent pipes. So, I took the screws out of the gray water valve and gave a little tug, and the whole assembly popped out. I cleaned everything and put the new seals into the black water valve and start to reassemble. Now hears the rub. On my RV, everything is glued solid, there is no give or take in the assembly and it's impossible to put it back together again without damaging the seals. The bitch of it is there is no space to cut the pipe and put in a union or some other device to allow me to reassemble the valves. My only hope is to find a piece of large diameter rubber or vinyl hose that I can clamp onto the ends of the fittings, thus allowing me to cut out a section of the ABS pipes to reassemble the valves. If this is unsuccessful, then I'm looking at dropping out the both tanks in order to replace these stupid seals. Who would design some thing this way?