Fuel tank modification.

[Le singe]

As part of my carburettor conversion, I'm going to need to fit a fuel tap to the plastic tank of my 1100.
Sourcing a tap isn't a problem, there seems to be a lot which use an O-ring to seal between the flat surface of the tank and the tap itself, and are attached by 2 bolts.
My question is: How would it be possible to attach the tap to the tank using the bolts without fuel leaking past the bolts?
I saw the photo supplied by Motomartin of the Australian bike with fuel taps,so it can obviously be done, but how?

 

[(RIP) Kaister]

i think the bike was merican if it was the black one.

The 2 std OEM ways of doing this is :

a - have the bolts inside the O ring - using a flate plate type mount
b - weld in a threaded boss and the tap has the captive nut.

so - using your plumbing background - why not a threaded boss from the tank and washing m/c type tap - 90 deg ball valve ( pingel type ) ??

 

[Le singe]

No plumbing background I'm afraid.
Been doing a search this evening and think a fuel tap using 2 bolts as a fixing would be easiest, these usually just have an O-ring around the fuel delivery hole, perhaps a Dowty type, (or Stat o Seal) under the head of each the mounting bolts inside the tank?