Fuel tank holes
 

Sorry if this is a stupid question, but my fuel tank seems to have an extra hole cut into the top of it and I can't for the life of me work out why.

I've got the filler neck hole, the breather port, the feed and return ports for the swirl pot, and then another hole on the top of the tank about 1.5" in diameter.

Seeing as it is the Marlin built tank, I'm sure its there for a reason...

Fuel level sender perhaps ?? Usually a big hole to allow the float to fit in .