Hot Water Heater ByPass

Originally posted by furpod If it bypasses the cold water fill side, then meets the T of the hot/exit side, and there is a one way between it and the tank, it will not fill.

Yes, but I'm not aware of a check valve in that outlet line. And if it is there that inhibits draining of the HW pipes and HW heater from the hot low point drain. All said I think the three valve setup, or two either/or valves, is best. Actually two either/or valves might be better since you would get either hot water, cold water, or no water, but not luke warm water.

Still can dump into the WH if it's been emptied. 

It seems that the single valve approach can still let some antifreeze into the WH, especially if the WH is already empty. I'm assuming the singe valve is an either/or valve on the inlet side. Pressurized red stuff on the bypass route can flow back into the WH through the unblocked outlet side. Yes?

In my experience, both can go wrong, and both can work. Using pink stuff insures there is no water left collected in a valve or fitting. I personally can do pink stuff in a couple minutes on our pod, while not all interactive time, it takes a half hour or so before I am comfortable when I have done just air. I do one valve at a time and let it flow at 30psi until nothing comes out besides air. Also, many people don't own a compressor.

Unfortunately, come spring, we will see several water pump filters, a few water pumps, toilet valves, and on newer pods, outside showers, all broken from not getting winterized fully, and my observation last year, most were people who used air.

Now, as far as the "why do people?"  I will never understand people that hook up and drag the trailer to a dealer and pay $75-300 to have it done. Regardless of what method they might use at home..

Interestingly the bypass system on my camper only has one valve.  That threw me at first but after thinking about it, it makes sense since it is like the valves in Matt's system, diverting the flow either to one outlet or the other.  The other end of the bypass hose just has a regular T fitting like the black one at the top of the pic, above.  I'm surprised more campers don't have just that one valve since it should be cheaper.