If using the three pipe system (more reliable than using an inline fuler on the feed line) one pipe goes to the fuling line, stoppered arfter use, clunk line to the carb (STBO) and the vent line goes back over the top of the tank and out the bottom of the fus left open to atmosphere, the reason for this is to prevent syphoning after manouves have put fuel into the vent line, hope that's clear.

Mike