Entry hole?
Yes, closing the intake should help. Once you get the bowl clear, that would help inject a solution like Sew Clean if the problem is that the discharge hose is clogged with scale.
(Ours, which had been working fine, apparently dried out while I had the system open for a few days doing other stuff, and that's what caused the scale or whatever to harden, serious clog. Before using the SC stuff, we apparently had just enough of a pathway through that water in the bowl would eventually siphon itself through the hose and into the holding tank.)
If you really have to do any take-it-apart service, you'll appreciate having pumped out/rinsed/repeated in advance.
Under normal circumstances, the macerator should be able to break up any solids... so that it's mostly a liquid going out through the discharge hose. If you have something in there that isn't turning to liquid or is otherwize blocking the macerator blade (wet wipe? etc.?), a plunger may or may not help dislodge that enough to capture it.
A plunger may be hard on the joker valve. Using it to "push" may be OK, but using it to "pull" may invert the joker valve permanently... Just a guess, though...
I was thinking of these threads, mis-remembering that they're actually two separate threads. In any case, see the especially the second thread, Peggie's post #26 which illustrates the clog:
http://www.trawlerforum.com/forums/s...tml#post589682
http://www.trawlerforum.com/forums/s...let-27621.html
-Chris