Be sure to purge air out of the vacuum hose line as best as you can before doing a final connection. I still vacuum old-school manually, so with the pump running, I lay the vacuum hose on the water, then I put one end of the vacuum line at a return jet and let that fill up the vacuum hose before I connect the other end into the skimmer. That's just one example.Besides turning the pump to 100%, is there anything else I should do when I manually vacuum the pool?