Winter Plug / Winterstopfen - Frame Pool

Preparing Your Frame Pool for Winter
Lower the water level until it is below the pump connection. Remove the valves and store them indoors.
Use winter plugs ("Winterstopfen") to seal the openings in the pool. This prevents dirt, insects, and other debris from entering.

I use them for my Intex Frame pool, "Intex Anschluss-Set Ø 38 mm"