Manual screen washer foot pump problem?

Hi there,

I hope I've got this in the right section :) I recently bought (from the U.S) an NOS manual foot pump for a screen washer set up on a 65 Valiant (Australian version) as the pumps available here are now extinct. Thing is the pump received has only one entry point into the bellows? not two as an inlet & outlet....can anyone shed any light on how it's supposed to work? It has the large nylon nut on the bottom as per the majority of Mopar manual pumps but only the one spout for the want of a better word.

Thank you :)