I'm missing something somewhere: I can't stop a vacuum developing in the tank. It has a lockable cap with breather valves, which I've stripped down several times to check/clean. As far as I can see, and gently testing with the end of a paper clip, the valves don't stick, and there are unblocked air passages through the cap, yet it still has a stonking vacuum when I come to re-fill it. I haven't blown then through yet, as a mouthful of diesel doesn't appeal, but it doesn't *look* to be necessary.
I doubt the vacuum is doing either the tank or the pump too much good, but I'm not sure what to do about it. Am I missing a trick with the filler cap? do the vents block/jam in some common but not-obvious way?
Baffled of Bristol.
PS: I've still got that new (petrol) tank - free to a good home - if anyone wants to collect it.