Thanks Everybody!!!
Lots of good ideas. I'll unbolt it, haul it outside and flush the jet
in reverse with a garden hose, shake it, hug it and so on. if that
doesn't work, I may go the acid or epoxy route. Having it outside gives
me all the options without damaging the pipes below.

I tried the drywall screw yesterday - , but the nut is just barely to
big - I had to unscrew it...