CPR bak-pak2 protein skimmer

I have CPR bak pak 2 protein skimmer used. I still have the old pump from the original skimmer. But it keeps from falling down and it ruined my tank. Like last night, I have incident and ruin my whole bathroom and my living room because of the pump is falling down while I was school. Currently I put the skimmer on the main tank. So I decided to change it. So my plan is that to put the new pump on the bottom of the back of the tank and use attach the pvc pipe on the skimmer. The skimmer is for 40 gallon tank. What's the best pump that is strong enough to do according to my plan.