RE: Perry pump?
Jay - I think that garRCfield is saying that you can use a one way valve in the tank vent line to prevent fuel from leaking out and still allow air to fill the tank as the fuel is used when using a Perry Pump. If the tank does not carry a neutral pressure, the pump will create a vacuum, and possibly collapse the tank walls due to the vacuum, and you will have will not get fuel to the engine. I use a one-way valve on mine as well.
I really should not answer for gar, and if that isn't what he's talking about, I hope he will respond and correct me as I would like to know how he uses it if it's not used this way.
As for the weight of the pump, not more than an ounce or two - they are very light. Just make sure that if your using a 2-stroke that you get the pump made for 2-strokes as those for 4-strokes are different, and make sure that the pump has a blue case as well as the older ones had red cases.
Phillip