I'll have to double check this evening what model I have (just remember that it was rated at 110gpd, 6-stage), I don't believe mine has a flush valve, if it does then I've never used it and maybe should be?

Though I will say this, my tap water measures at 380ish TDS, and I got a consistant 0 TDS from it for the at least the first 2K gallons of filtered water, when TDS hit 3ppm I just changed the resin and she's right back to 0. Now I'm pulling over 100 gallons a week from her, generally have it running 24x7 5 days a week (crappy line pressure is around 30 PSI so it takes a while). But in all honestly if it caught fire today I'd have another by the weeks end, and in no way feel like I'd been ripped off.

I'll check this evening when I get home and post it in a few hours, unless someone else chimes in before I can get there.