Now, while I don't have a solution, nor answer as to why the drain holes were designed to be in the locations they are, nor do I have the answer as to why the moron that drilled the holes drilled them 1" too high, how's this? Drill a 1/2" hole in the bottom of the box, directly below the drain, and insert a rubber plug? Keep plug in during the season, remove when laid up? I mean, pretty simple, and pretty cheap...
nor do I have the answer as to why the moron that drilled the holes drilled them 1" too high,