There is a picture of the underside of the tank here
link
I know I've figured it out before, what that triangle guide was for, I just don't remember what that was.
Maybe a support for setting the tank on a flat surface when off the bike or to help guide the lines as the tank is lowered ??
It is item 18 in the Fuel parts diagram. They just call it a bracket.
Nothing goes through that guide so that's probably why you don't remember removing anything from there.
The vent lines run through the white plastic guide under the tank then under the radiator hose, then through the 2 guides up front on the left side of engine.