On my 89 Overnighter, there was a 6" screw-in access cover on the sidewall by the floor drain. With it open, I could reach the thru=hull and with a little contortion, the floor drain. To replace the fishbox drain, I ended up cutting a hole in the bottom of the fish box and covering it with a 6" cover. I would not have been able to reach if I'd cut through under the seat. It was a real bear to get the elbow off the hose and the new one on. Can't imagine triyng to do it from any other access.
Gary 93 Gulfstream :hmm