You didn't specify whether or not your trash can and sump are on the same floor. If so, the first thing you should do is invest in some rollers for your trash can. Example: the brute series of trash cans have an optional accessory (rollers) you can purchase separately. My local Home Depot carries these.
For my system, I have a basement sump and first floor tank. There is an extra tee from the sump pump going to my utility sink. To do a water change, I simply turn off the flow to the tank and open the valve to the utility sink. This drains the sump using my return pump. Then, I turn off the pump, use a maxijet to fill the sump from the new saltwater (brute trashcan on wheels), and I'm ready to go again.