My panel has three hole as well. BUT a friend near by has a 1/2 panel and his does not. The bottom "catch" that bolts in this area is an "odd" shape but I can't, or haven't figured out just way yet. I am at the point of putting them on but have a couple things ahead of it. I'm wondering if perhaps on some panels there was a different kind of "catch".
It is interesting. Here is a pic of MY catch in place and you can see the other hole is probably the one your talking about.
http://i140.photobucket.com/albums/r19/LutherParris/52Panel/000_0201.jpgThis is a picture of my FRIENDS bottom catch. You can't see a 3rd hole on his unless its full of dirt and I wasn't checking for the hole when this pic was taken. I only wanted to know what kind of catch it was suppose to be.
http://i140.photobucket.com/albums/r19/LutherParris/52Panel/RearBottomlatch.jpgPersonally, I don't think its a drain hole.
