What have you done for a breather for your fuel tank? (and is it likely to be acceptable for IVA?).

Looking at the Mocal fuel tank breather from Demon Tweeks, however I'm wondering if it is necessary or is there a cheaper option?

I used this passed IVA no issues

linky

any car spairs shop will sell a one way valve mine cost me £2.99 I think mounted with a lenth of fuel pipe done

You need a two way valve to allow air out on expansion and also air in to allow fuel to be pumped to engine. The valve also needs to close when car is upside down.

I just use a hose with a very very narrow restriction. It works well.