You have to blow 6 gallons of air out of the Hot Water tank and fill it with 6 gallons of water. I don't remember the flow rate of the pumps but it takes time.
We don't drain our system after use, only at winterization time. We sanitize our system at the beginning of the season and call it good. I usually do drain our fresh water tank each time, depending on where we picked it up and when we are using it again. Iif it's been a while since we have used the Pod sometimes I will hook the hose up to the city water inlet and flush the Hot Water tank.
Something else we often do is put put a small amount of bleach in the water a when we fill the tank. (about and oz and a half) When we bought our Pod about two years ago I found some "fresh water" stuff which turns out to be bleach. I have it so I use it but any good clear bleach should work. (no aroma additives or such).
We use bottled water for drinking and coffee. (I'm a little fussy about the taste of water) The small amount of bleach in the water is undetectable. If my wife can't smell it................ No problem.