Welcome!
I can only tell you the theory: The IG pool folks can tell you the practical. Seems you have to blow out the line before you plug it, to get the water out, but I've not heard of a one-way plug. You may want to consider putting non-toxic pool anti-freeze in the lines, too (they use the same stuff in the water tanks on RVs and in cold-climate solar hot water heaters.).

Beyond that, I'll let the experts pick up.