exudedude, I have a 1990 Gulfstream, just replaced all the thru hulls last year. The sink drain fitting was located to the left of the sink about in line with the bulkhead. To access this I believe I removed the bulkhead to the left of the cabin door. Not a bad job at all. If there further towards the stern you can also remove the draws under the port seat where the fresh water tank is located. Good luck