Here is my take Rob. Yes to bypass, no anti-freeze in WH. I flush twice a year, in Fall and again in Spring. In Spring, after adding bleach to fresh tank, flushing system, WH still by-passed, I now open WH by-pass, and add the bleach water from fresh tank to WH, allow to sit over night, flush WH, and drain everything. Now add fresh water to fresh tank, drain fresh tank. Refill fresh tank, run through all faucets, and fill WH. I'm now good for the season.
If I am not going to use the camper for a few weeks, I drain the water heater. By draining, not leaving heater full, it seems to greatly extend the life of my anode rods.
I always keep some water in fresh tank, during season, and the black tank also.
I do put teflon tape on the anode, and keep it installed over Winter.
If you can understand this, I hope it helps! :)
Jerry