on the 1991 it was all but impossible... I was able to reach it from the aft cabin after taking out the batteries, and moving almost all the plumbing not related to the tub drain...I then ran a snake down the drain and could hear it in the hose. I cut the hose as it entered the engine room, and then tied and secured the "new" hose to the old one, which in my boat dumped into the shower sump box at the base of the stairs...
then went back to the aft head and spliced the new hose to the old hose....I did not see how you could replace the drain itself, unless you unscrewed the strainer and the "whole" assembly came out in one piece...you would then prefab, sting mount a gasket and reverse the process, add some plumbers putty to the strainer and put it back together.
I was not brave enough to attempt that, as it was pure speculation and the folks at Hunter had no firm info one way or another.
BTW, if you do this, take the time to service, inspect and reclamp the vacuum breaks and cockpit scupper hoses, work the thru hulls...as all of that is impossible to reach without taking the batteries and boxes out.
Pays to be thin, or con one of the kids in to helping...
