Fuel tank plumping?

[Paul Hill]

Plumping in the fuel tank has made me stop and think as this is my first model with petrol engine with a fuel pump, all my others are glow engines using pressure from the exhaust to pressurise the fuel tank and feed the carb. In the past I have only used two pipes from the tank, one to the pressure nipple and one to the carb, the carb feed line goes via a two way valve to enable filling and prevent flooding of engine. With the pressurised tank and a good working clunk pick up I've never had any fuel problems regards which ever way up the model is.
With petrol the fuel tank is no longer pressurised, the clunk pick up is fine BUT how do I vent the tank for both inverted and normal flight, two vents one up one down? what stops the fuel leaking out the submerged vent?

I'm sure there is a simple answer.

[John Townsend 389]

Paul, only one vent/overflow is required, with the engine running there is a negative pressure in the tank so the vent acts only one way and when not running, as you will have the end of the fuel tubing from the vent/overflow below the tank(generally dangling below the fuselage), when inverted the fuel will not run out of the end of the tube which would be then higher than the tank.
John