it's a 50 gallon stainless steel tank located in the bilge. has a large square inspection port on top - maybe 6" square - held down with about 20 screws all around. the plate has a i/2" nut located on it which you open by hand to drop in the fuel guage stick (no electric fuel guage for me!). the gasket was a large square piece of some kind of neoprene. i found a good neoprene replacement at an auto parts store that i had to cut to size. been on there for a year now with no problems. i think it's better than using rtv or some such compound because you may be opening and resealing that hatch more often than you think....