I had a funny little drainage hole in my boat. It had like, a little flange on the outside of the boat that the plug was supposed to grab onto, and pull tight against the boat. Couldn't figure out what kind of plug worked with it, and I tried about 5 different plugs from walmart and BPS, and none worked. I just cut that mother off, got me a rubber plug from lowes. And it works perfectly.
I got the idea from a member here when I first found the forum. Goes something like this.
Take the rubber plug, and drill a hole straight through the center, use a bolt with a wingnut, and a washer on each side of the plug, place in drainage hole, and tighten down until it doesn't leak. Works like a charm.