X5 on the saw hole plug! Been dealing with it for 3 years! My solution was to install a twist on third valve on the hose connection out side the wet bay. When the gray blocks up I ensure the gray valve is open...close the newly installed third valve and open the black valve for about three seconds. The black water, assuming you had some in the black tank, forces the "air bubble" trapped between the three valves up through the gray valve and blowing the plastic disk away from the opening. You will hear the effect that is happening as a loud bubbling. Now ensure that the black is closed and open the third, exterior, valve and WHOOSH...the gray drains. If you have a problem with a little black water perhaps getting into you gray tank you can always drain the black and fill with fresh water from the tank flush system before performing the procedure. It's a pain in the butt but it's better than spend a lot of bucks on having the belly opened up at a dealer to try and get it fixed!
2011 Georgetown 378TS in FireMist
2013 Jeep Wrangler Toad
Kirby the Old Dog, passed but still in our hearts
Max E. Dog, the new pup
Eureka the Old Cat, still hangin' on