An older PCS Orion... the boats made a few years later had a small manual pump at the galley sink for pumping out the drain hose. I plan on doing the same thing.

But first I had to find the drain line... I put water in the box and followed it back... it turned out the hose was really quite accessible, just hidden by some furniture and trim. But I could not find it initially... until I made a stream of water that I could follow back.

You might try just some food colored water in the drain and see if you can follow it back from the bilge... you may be surprised to find a small hose just under some trim in that back area.