Dear OCD,
Flushing your tank isn't going to make it "clean". It will help if you didn't use enough water in the tank to begin with.
We've have our MH for going on four years now. When we were new, we did all sorts of things. Flushing, GEO, ice cubes and a few other things probably. Over time and watching the tank a little bit, decided most of that really wasn't necessary, just use lots of water to begin with.
Sometimes after dumping when about to leave an RV park, I'll put in 5 - 10 gal of water. Then after 4 - 6 hours of driving and the water sloshing all around in the tank, the water action saved a lot of water and it saved my time messing with it. 4 - 6 hours of water sloshing all around in the tank beats 10 minutes of using a tank cleaner.
When out dry camping, we put the dish water in the toilet. This saves on fresh water and it makes the smaller grey tank last longer.
Bill