Saltwater mixing container

I am using a 32gal Brute container to make saltwater in, and I need to make 20gal of saltwater per water change. I have a pump inside the container similar to the setup used on ReefBum.com. The problem I have is though the last 5gal in the container are what submerge my pump. If go below that then the pump is out of water. The tank is much higher then the container so any recommendations on transferring that last 5 gallons of saltwater out? Thanks