This was located at the bottom of a port fuel tank on a year 1986 boat. There was an identical device at the bottom of the starboard tank as well. Any ideas?
Maybe. But where does it pump to? And what is with the chain? Seems like the plug or nut on the bottom is meant to be removed and replaced since its attached by a chain. But why would you need a pump at the bottom of the tank?
I too think it’s some sort of drain at the bottom of the tank. I’d guess that you remove the chained plug in the bottom, then push the plunger down to open the valve and drain off any water or other crap