I have an MK ally tank. At the right hand end there is a small vertical outlet, about 6mm in diameter. It comes out the top of the tank and until yesterday was connected via a piece of rubber hose to a similar outlet on the back of my fuel filler neck (a black plastic Tifosi one).

Unfortunatley I managed to snap the plastic boss off the back of the tifosi filler neck last night.

So:-

A) what can I use to seal the plastic hole in the filler neck?

and

B) what should I have connected to the tank breather? Some sort of air admitance valve?

Mike

If it's anything like my set-up the pipe coming out of the filler neck acts as a drain in case the fuel blows back whilst filling up - probably a good idea to keep it. If you need to blank it off some of the two part plastic metals (JB) should suffice.
IIRC the tank breather should have an air admittance valve for comp. use but if comp isn't a prospect fixing the pipe and exiting it below the bottom of the tank should prevent drain down in the unfortunate event you roll it.
HTH.
Cheers, Pewe

[Edited on 7/6/10 by pewe]

I was also going to suggest some of JB's finest product