In particular I am re-plumbing the galley sink. Had to do it for two reasons... could not get access to the refrigerator compressor otherwise, and the darn thing was a witches brew of bad parts waiting to fail.

The stainless steel sink and faucet are in very good shape... the sink was only held in place with RTV... not the bolts on the underside. (I was just baffled looking at that...)

RTV and PVC seemed to be all that was keeping the sea from flooding my boat. The thruhull is a good bronze through hull with a backing plate, into that was a marlon threaded piece with a hose nipple. Onto that nipple was double hose clamped a nice chunk of rubber hose... from there on up to the sink drain was a disaster. Crappy commercial PVC (the thin white stuff) with rigid hose all clamped and RTVed together... parts of which just fell apart in my hands. (good thing I like to keep the thruhulls closed.)

So the first question is are there marine grade sink drains available, with proper hose fittings, and can these be T'd together for a double sink.

Can I use plumbers putty where these sink drains meet the sink itself... or is there something better?

Yes, in normal use, the sink is above the waterline... of course on a hard starboard heel, that may not be the case.

I'm going to run down to the local marine supply today to see if I can get some local answers... but I may have to order some things.

Oh this deserves a proper picture... you guys need a good laugh. But I took it all apart before I photographed it... Probably best, as the evidence is just sad... oh so sad.