lake navajo

I just bought an astroglass 1987 178v with a 150 evinrude nice boat solid transom solid floor etc. their is three plugs on the back of this boat 1 is for the main drain I am not sure what the other two are for the fella I bought it from was not a fisherman he was a joy rider and sealed them off with silicone so they would not leak what are they for this is my first fishing boat other than a canoe can any body help. Loren G i n Durango, Colorado