Well, I'm learning
I did have the transom mount opening filled in, and by accident the drain hole was plugged from the fiberglassing. I had a funny problem where the gas tank and propane tank mounted on the platforms in the cockpit were held down by a stronger type of all rubber bungee cord, kind of like a snubber. They were connected to eye bolts; but the bolts had become very very loose and much larger holes than the original drilled existed. When the cockpit filled with rain water, the water continued down into the transom storage area; then the water flowed through the eye bolt holes into my boat filling it with water (about 14 inches), during one of our long fall monsoons we get here in the Pacific Northwest (or West Coast of BC).The solution? First I took out all the eye bolts and filled in the holes. Secondly, I had installed scupper filters to keep out the shells; the shells would plug the hole from draining. I had the old drain hole re-drilled to a much larger size. Finally I added another through hull in the transom. I had the two scuppers connected by rubber tubing (the same as sink tubing) so the tube ran across the back from scupper to scupper (abeam). Tee'd into this hose was another hose going to my new through hull. So I have separate drainage for the cockpit, so it doesn't flow into the transom storage area. And I have a drainage through hull (the old one) for any water that might make it into the enclosed transom storage area.I've been researching and the chap in "This Old Boat" - Don Casey - says:"A check valve might initially keep the water from draining back into the bilge, but deposits of debris and detritus from the bilge water will soon prevent the valve from sealing. Besides, a check valve in a bilge pump discharge line is a bad idea because it reduces the output and introduces a real risk of blockage." (p. 281)I was panicking about putting a through hull in an area above the water line, it just didn't sound like good seamanship; however I have now found a couple of references where a through hull can be fitted high on the boat. Sounds like a good idea to have one fitted high and near the stern.I see Casey also recommends a very large electric bilge pump (around 3,500 gallons per hour) that can be turned on and off with a switch. Since I will have four gold cart batteries installed and my inverter, I think I will use my new electric bilge pump I bought from home depot on hand to plug into an ac outlet if larger volumes come in from whatever crisis I have on hand. This larger bilge pump came in handy when I had my boat flooded, and kept re-flooding until I discovered where the water was coming from.In one document I printed out from the web, the author recommends wiring the electric bilge pump(like the Rule pump) directly to the battery, with in line fuse. He says many of the boats he has seen filling with water occured because the fuse, or trip didn't work, the bilge pump was therefore turned off by the faulty problem and the boat filled.I have also seen that a boat my size (27 feet) should have at least two pumps, preferably three.