you know , I don't even know the name of these animals.
I'm looking for waterProof inspection plates or cleanout hatches for water and fuel tanks. It isn't the usual screw-in bronze or plastic deck plate. What I think I'm searching for are plates with multiple bolts that pierce the tank where you want the cleanout and have a lid held semi-permanently in place with nuts and a fancy rubber gasket.

Henderson in the UK makes such a fitting (tho I have not actually seen it) that has fuel attachments in the plate: level gauge, vent, supply. I have Not found a US maker or distributor. It seems to me to be a very good product.

Especially if it is available for gas tanks.

Tho I could use a similar one for water tanks. Help, anyone????????