Removing complete gas cap assembly... warnings?

[stopintime]

I need to fill my tank with some flame inhibitor foam (planning long strips)

Easiest way to get it in, and especially out, is through the gas cap - if I remove all of it.

Procedure tips?
I've seen pictures of some small retainer allen bolts (which I'm sure I'll strip) going outward horizontally into the plastic, or maybe that was a metal tank. What will break, fall into the tank, .....  ?

[ducpainter]

The plastic tank only has a small opening. The metal retainer is molded in.

I'd remove the pump and stuff it in the large hole in the bottom. Get a new o-ring if you go that route.