Drain hole in keel?

Hello, I’m working on my Irwin 30. I dremelled into what I thought was a seeping blister in my keel (about half way up the keel about two inches from the back edge). I ended up finding a small plug (less then a dime in size) just below the surface. The plug was ‘plugging up’ an obvious man-made channel (the channel makes a quick turn so I can’t see see very far in). I’ve googled without finding an obvious explanation of what this could be. A drain for the keel? Should I leave it…Drain hole in keel?