"leek"
I do not have a "water tank" as such on my O'Day 22..What I do have is a 5 gal. water bag. The "bag" is free, not attached to the hull. If the bag did leak (which is quite likely) the water will collect in the bilge, above the keel. As far as looking for a leak, the most likely spots are the windows, the toe rails. If the leak is at the water line or below, I would look at the lower rudder fitting. Short of a crack in the actual hull, I would take a look at the outside of the keel. It is possable that if you have hit a rock or something and damaged the fiberglass in the keel area, water could be getting in there.If you would like to discuss this further......skyking22@aopa.netGood Luck!Warren