Some of the older boats had a pump up in the cabin drain area ...does the water flow to a well area forward where a pump could be or once was mounted ? On the 311 there is a thru hull fitting thru the rear of the back seat ... On Jeff32's pic of the drain ...go up about 2" and then a hose attaches (about 18" long) to the thru hull and and just drains into the bilge .... I would plug the other drain and drain it like the 311 ..... I'll get a pic ...

Look below Starboard trim pump ...this pic shows the hole without the thru hull ... and then a short hose that turns down after the deckplate .....m

offthefront! You really did a nice looking bilge job!