You could run the pump with flex tubing that is long enough to put it up into the main tank for backwashing. Basically, it will run out of the sump normally, and then when it’s time to backwash, you would simply move the pump up into the main tank and pull water from there for backwashing. Since your ultima will be after the sump, almost all of the debris will have already been filtered out, so you will not need to backwash very often. If I had to guess I would think you could get by with every 3-4 months between backwashes.