how to replace holding tank dump seals on 2000 u 320
Merry Christmas and Welcome to the Forum.
Hardest part of replacing the dump valve seals is getting access to the valves. Different on every coach.
Removing Your Holding Tank Valves for Service (http://web.archive.org/web/20200111052652/http://beamalarm.com/Documents/Removing_your_holding_tank_valves_for_service.html)
Make sure the tank is empty before starting work. Tilt the coach to opposite side to insure no tank contents will spill out.
Once you get to where you can work on the valves, simply remove 4 bolts, remove the valve, replace the seals, put it back together.
https://www.youtube.com/watch?v=2lJsQ_Sldjo
Use lots of silicone plumber's grease on all the rubber parts. Test the action to be sure there is no binding. It is easy to get an ORing seal out of place during assembly, if you do it will leak. The silicone grease helps hold them in place during reassembly.
I put a 1/2 sheet cake pan under the valves to catch any seepage. Find a pan that will fit.