Old Dickinson heater w/tank how to fill?

[Sea Dreaming]

We have an older Dickinson Chesapeake heater, it came with the boat and we have never used it. How the heck do you fill the fuel tank?

The only opening besides where the fuel feeds out is a 1/4" hooked, brass tube at the top of the tank. The manual has no info.

Thanks!

Just after I posted the question hubby realized the tank slides out from behind the heater and there is a capped opening at the top of the tank. Duh!

Still, I will leave this question up just in case someone else needs an answer to the same question.