Didn't see any mention of this, but maybe I'm missing something. I haven't used my new Mini in the field yet (I'm just a 3 seasoner), but back flushing at home in the following way seems to work in the controlled environment.
Since I carry 2 SmartWater bottles, I have one of them capped with the flip lid that comes on the smaller, 700mm size bottles. The nipple of the cap fits snugly over the nipple of the Sawyer. So my plan, at least for the short trips I do, is to just fill up my bottle from the filtered dirty bag, put the cap on the bottle, remove the bag and stick the bottlecap nipple over the outflow nipple of the Sawyer and give it a hard squeeze. Figured I'd do that every time I fill up, just to stay on top of it, and it wouldn't take any extra work at all anyway, so why not?
Nothing extra carried at all, since it's all built in to the system anyway. It works this way really well at home. Lots of back pressure with no leaks and no clumsy connections. Time will tell how it performs under adverse conditions I guess. If anyone knows a reason why this wouldn't work well, please tell me now!
Edit: I do realize the hinge on these cap are weak, and I've had them wear out before, so for drinking, I'll just be unscrewing the cap just like a normal cap would be used, and only flipping the lid to expose the nipple for flushing. Even if the cover does break off, I'd just swap out with the cap I keep on the dirty bag for the remainder of the trip. I've swam in enough lakes and ponds to not fear droplets of "contaminated" water.