I haven't had any issues out of leaving it in the tank for 2-3 days. If it's gonna be a day or 2 until my next job I put a damp OP towel over the top of the tank. I always top off the tank (and add more concentrate) before starting another job though... That said I wouldn't leave it in there for a week... The water may evaporate & leave a bunch of polymer in your machine and clog it up... I usually rinse the tank/flush the system before storing for more than 5 days as a precaution.
If you have a full tank you want to save for an extended period of time a jug with a cap is probably your best bet. As long as the jugs is s sealed I don't think it'd be a problem. Worst case you add a tad bit more concentrate.... It's not like it's an oxidizer that's going to fizzle out in 45 minutes or an hour. Just label the jug so you don't forget what is in it. lol
Totally on board with your spot on machine maintenance. Got myself in the habbit of flushing the Orbot power spray completely with hot water after each use before storage.