Good Morning, You just need to keep your membranes wet upon storage. If you have a flush kit, use it, before storing.
Depends on your water pressure, if you have enough water pressure to run the waste into the Piggyback; then you will basically cut your concentrate in half. If you have higher pressure then you will see a better result. Pressure is a factor that determines efficiency. So; the second membrane will produce 4 parts BUT you get twice the output. So you the overall is 2 to 1
Water quality is important as well. If your water Quality is bad, running the waste into another membrane will beat up the 2nd membrane faster.