Momentary switches work fine. They have 3 prongs. 12V when forward, +12V, and 12V when backward... the 3 position switches. Hook +12V from the battery to the center prong. Hook a fill valve to the front prong and a dump valve to the back prong.
The switch will have 3 prongs, where the middle one is the power source, from the battery. The other two prongs go to your valves, and your valves have two wires, a postitive, and negative. Ground the negative, and hook the positive up to the wire from the switch.