I am working on a neighbor's old flat bottom (1432!). He can't find the source of a leak at the drain tube. I dunked it in the lake earlier and it appears that the tube is flattened out a little by maybe a gas tank laying on it or similar. What have you guys done to fix something like this? It's not a bad leak...he said it takes about 4 hours to have a cup of water in the boat, but he hates leaks. I tightened up the drain plug as much as I could possibly tighten it and it seemed to help but still dribbled a little. Any ideas?