Stan,

It is not generally a good idea to use your receiver battery for anything other than the receiver and servos. You wouldn't want to chance losing the plane because the pump drew the battery down prematurely.

My buddy has one of these powered by a 120 fourstroke. He runs smoke so carries the extra weight of pump, tank, and auxiliary batteries around. It flies great. He is at half throttle most of the time.

Add the extra pack for the pump. You will never regret adding it but you could regret not adding it.