Raybo- I flushed my tomatoes with the Clearex once last year around late mid season. Per the advice of my good hydro buddy I poured the flush from the top and removed the excess/drainage out of the reservoir after allowing to fully drain. I think it all depends on the fertilizing schedule. The more often you fertilize the more often you might want to flush. I under fertilized most of my stuff in SWC's last year and had to supplement with FP or MG so I didn't see the need to flush more than once.
On a side, did you hear about the northern arctic storm coming later this week? They say its going to get really cold here with a slight chance of snow.
Damon