I have a hot tub and there are two pumps connect to the tub as indicated in the picture attached. But, there is a extra flex pipe (open end) stick out in the ground and which is connect to the hot tub as well. When I winterize my hot tub (blowing from the hot tub's jets or return), I can see water shooting out from this extra pipe which means it connects to the hot tub. Anyone know what this pipe does? Thank you very much.