Green’s Dictionary of Slang

foo-foo valve n.

(Aus.) the anus.

c.1943		S .J. Baker Aus. Vulgarisms [t/s] 9: foofoo valve: The anus.
1959		D’A Niland Big Smoke 1277: ‘But let me drop dead tomorrow and that cow would bust his foofoo valve scrambling to get to you first with a proposal of marriage’.