I'm going to get beat up pretty good on this next statement I'm sure, but in all the years I've owned travel trailers, I've never sanitized my lines. When my parents owned their travel trailer from 1963 to 1983, sanitizing wasn't even though of. They never had problems with the water system in that trailer. I've never had problems with any of my tanks either, or water lines. I think that's because we do enough variety of camping that we do occasionally get hooked into city water that is chlorinated and treated, and that is sufficient to keep the system functioning.
Another item to consider, we use our water tank 100% of the time when camping. It's drained every time we're on the road. Refilled at the next location. We never attach the garden hose to the camper. We always fill the fresh water tank and use the on-board pump (no danger of EVER over pressurizing the lines or experiencing low pressure water at the campgrounds this way).
Do as you wish. I'm not against sanitizing, it probably is a good thing to do the first time you use your tank to clean the factory chemicals out of the tank. But after that, it's really all about YOU and YOUR comfort level. But "necessary?" I personally do not think so.
Back to your original question about flushing the "pink stuff". You are absolutely correct. Keep the water heater in bypass until your lines are clear. Then open the bypass to fill the tank.
Flush the lines at each faucet until you see no more pink, and no more foamy water. Once the foamy water ends, taste the water, I use just my finger tips, that's enough to taste, takes only a split second.
And yes, you want to make sure your low-point drains are cleared also. They catch a small amount of the "pink stuff" that will continue to mix with your fresh water. Although it won't hurt you, it will cause your water to continue to be a bit foamy every now and then, until it get's mixed completely and replaced with fresh. If not drained, it could continue emitting residues of pink stuff into your lines for a long time. Here again, it won't hurt anything, but it only takes a moment to open the low points and drain it there. So why not?
By the way, flushing each line, each faucet, hot and cold, and the toilet, takes only about a minute for each faucet. Once all the lines are clear, do it a second time, in the same order. I find this helps a lot, as sometimes there still might be a bit of foam. All you are doing is running water through each outlet until all the pink is gone. Just that simple.
