Is the pump you have reversible? If it is, the pump should pretty explicitly say so. If the pump isn't reversible, you can't do it the way you're talking about.
If it is reversible, you'll need a 3-way sway, 6-blade switch. Wire the battery leads to the middle blades, wire the pump leads to the top (or bottom) blades, and then wire some crossover leads from the top blades to the bottom blades.