Can you use flock with a cartridge filter?

When you use flock you should not put it through the filter.When vacuming flock out of a pool with a sand filter you vacuum to waste. However you don't have that luxury with a cartridge filter. The ideal solution would be to put a 3 way valve between the pump and the filter and set it up so that one of the ports can be run to waste while at the same time shutting of the water to the filter.