You don't say what year your boat is, but I'm guessing it's an early Moesly version, late 60's vintage like this:
http://www.moeslyseacraft.com/20-cc-seacraft.html Check out the brochure - it says there was a 40 gallon tank under the console seat.
You may also have a bait well under one of the stern seats like my boat had with a water inlet/outlet right at the transom. It was fed by a 3/8" copper tube that slid down through a couple of brackets on the transom and extended just below the bottom of hull; had a 45 degree cut on bottom end and top of it curved around to fit into a 3/8" hole in the transom right at the water line. There were a bunch of 1/8" diameter holes surrounding the 3/8" center hole that let the water back out. There was a plastic cup with a screw in cap about 4-5" in diameter inserted into the transom in that area and bonded to the outer skin to seal the holes from they plywood. If your transom has been redone, it may no longer be there, as they tended to leak and rot out the transom! Fortunately I checked mine shortly after getting the boat, repaired what little damage there was and resealed the whole thing with epoxy. I thought it was a clever Moesly idea that worked well and did not require a pump. I believe the 20' that Strick restored was one like that.