I have been looking at various plumbing schematics, to understand them so I can plumb my panels to pool. I have run across something that I can't understand. In all the schematic designs the thing I don't understand is in all the designs. So I am not able to use a different method, so I am hoping someone can first, understand my question, cause I am not that good of an explainer, and second tell me how this plumbing set up involving the three way switch, the filter and the one way flow valve works together. Here goes nothing. This pertains to fully being able to drain the panel of water in winter, so water will not freeze and break pipe. But in the four schematics above, and all the others I have seen, the problem I can't understand how it works deals with the water pipe leaving the filter, this pipe carries water from filter, to and through the one way check valve, to and through the three way valve. Now if I try to drain this section of pipe, I would first open the three way valve to allow the water to drain down to the check valve, back to the filter, then drain the filter of this water. But how can the water that is between the three way valve, and the check valve, that only lets water run through it in one direction get through the check valve, to drain back to the filter? Seems the water would be trapped above the check valve.
