That depends on the valve you use. With a more expensive valve like the one from Greasecar, you can use a normal on/off switch. In one position the switch would provide 12v, in the other there is no power but the solenoid returns to the other tank due to having a spring.
If you use a more common Pollock valve then you will need a on/on 2 pole switch. What that means is both positions are on and you are switching two different items at once. You will have 6 connections vs 2. Picture the connections like this...
The lever of the switch either moves up or down, connecting 1 to 2 and 4 to 5 or 3 to 2 and 6 to 5 in the other position. What you would do is connect 1 and 6 to ground, 3 and 4 to 12v and 2 and 5 to the two legs of the valve. When you flip the switch one way, 2 will supply 12v and 5 will supply ground. The other direction reverses that so 2 supplies ground and 5 supplies 12v. This is necessary to reverse the current and make the valve move in both directions. Alternitavely, some switches have a bridge making these connections for you but they are harder to find.
If you want to get really fancy, you can do like I did and use one of each type of valve. I can manually select one tank for return and one for feed so I can run the pump and transfer fuel between the two. Makes it easier to drop the tank that way.
Last edited by JSchuricht; 06-29-2013 at 09:46 PM.