i have a pool, round 18'x52", on level ground w/ a sloped hill behind it about a5 ft away. my idea is to use the bottom drain hole on the pool to move water into a 50 gallon sealed barrel filled w/filtration foam, (to be located below the level of the pool on the slope) and to move water from the 50 gal. barrel back up to the top back into the pool. how do i figure the drop to give enough pressure to bring the water back to the pool ? please help....Pat