For the waste Y valve, you'll most likely need to remove the valve and disassemble to repair the valve. Obviously, this requires the boat be on dry land. You might just as well replace it.
I dont have a table, so I have no experience in that area. Seems like a large pipe wrench and some brute force might do the job. This does require removing the table top from the legs first.
Otherwise, I think Dennis covered it.
