So I thought about this more and went ahead and pulled the T-Stat and reverse flushed the cooling system by blasting water through the t-stat neck out of the lower hose. I used a shop vac to then blew air the same way until it was pretty dry.

I didn't see anything besides watered down coolant come out - no sediment or gunk. Since this system seems pretty clean, should I bother with using a flush product at this point or go straight to the ceramic sealer? I am pretty confident that there is pretty close to zero anti-freeze left in the system and I had no issues with my heater core as far as lack of heat.

I am trying to avoid having to put the t-stat back together, running the car, then having to tear it down (while hot) to get the flush out completely so it doesn't sit in the system. Am I asking for more trouble using a flush product? Or should I just use it since I bought it?

What about leaving the t-stat out just for the flushing process so I can just pop the hose to flush? My car has AC so one of those housing bolts is a PITA to get on when the motor is nice and hot.