Should be a description in that TOTM write-up.
Basically she has two 55 gallon plastic barrels. She fills one with RODI, dumps in salt, and mixes it with an external pump that sucks water out a bulkhead at the bottom and dumps back into the top. When it's time to do the change, she opens a valve that diverts her return pump flow into the second 55g barrel (the waste barrel). Then by turning a valve, the mag pump that is mixing the new water is diverted to pump water out of the bottom of the fresh barrel, into the sump. When that's done, she turns another valve to use the same mixing pump to empty the waste water into the sewer drain. Very slick.
Nate