Thanks. I would have thought that would work, also. I did use one of those (this one is called a Drain King). It did it's thing, made the pulsing sound, expanding and releasing. I let the hose run for 20 minutes with no success. That's when I got the idea that maybe there was a check valve in the line somewhere. But it could also just be pollen and fir needles caked up. Lots of fir tree branches over the pool. If pollen sits on the bottom of the pool for more than about 5 days, our robot-vacuum won't even get it off. I have to used the stainless-steel brush on it. So I know that pollen can stick and harden.