I use a mag utility pump...it works great. A hose is attached to the pump and run up to the tank. I have an auto top off unit that tells the pump when to come on and pump water.
The ATO has two sensors, one for the tank at the level I want my water to stay, and another in my RO holding tub. That sensor won't allow the ATO to pump if the water level is too low, to protect the pump from burning up.