Why do you want to replace it?
I have a 322, so not sure if it the same as the 302… but on the 322, the holding tank sits under the rear berth. Remove the cushions and look for a piece of plywood that is screwed down, remove the screws and lift up the plywood. My tank is there. The pumpout hose runs from the port side deck, down inside the lazzarette, and down through the bilge behind the engine. Mine runs alongside the tank, to a 90 degree fitting at the bottom of the tank. The waste hose from the head runs along the rear engine bilge and connects to a fitting at the top of the tank. The tank is small…about 19 gallons.
I have lifted mine out, took it home and washed it out. Then I rebed the inlet and outlet fittings (they screw into bosses in the tank.
Here is a little video I made….again, this is on an O’Day 322. Not sure if the noO302 is the same.
Greg