Ben, here is a link that might be helpful to you. Batteries in parallel The Parallel Wiring Example shows how the batteries are wired. It will give you the same voltage with more Amp Hrs.
run a battery cable from the - negative of one battery to the - negative of the second battery, do the same with the + positive terminals, then hook the load ( lets say your 12volt pump ) to the terminals of lets say battery #2) and like Chris said you'll have 12 volts and more amps .this is called running the batteries in parallel