Pump for drain reservoir???

I'm trying to find a pump I can use to pump from a reservoir inside my tent to one outside. Temps inside are way to high so I want to drain to one res and when the level gets to a point, pump to one outside. Basically a sump pump but would rather have something smaller than what I'm finding. I thought I saw a aquarium related pump a while back but I can't seem to find it now. Any suggestions?

I keep my rez's out side of my cabinets to reduce temps and increase valuable space for plants. Any pond pump will do as you are just moving water without pressure? Once you want pressure or to pump up (refered to as the pumps head) you will need a higher end pump. I would suggest any inline pump as they seem to build less heat in the rez.

Ok, but what are you using for a level switch? What I'd like is when the smaller res inside gets to a certain level, it turns on the pump to the outside res.