The Holley pickups come two two a kit. You can buy more pickups if you want. Put one pickup on each side of the tank, or in all four corners. Each pickup has a filter screen material over them, and each pickup has a one way check valve, that shuts the flow off if it does not have fuel. Fuel will be flow from the pickup that does have fuel, not air. I'm not sure if this answers your question, I would hope it would. If you are not sure what a check valve is do a google search. Also, there are many threads here with information on the Holley pickups.