:joy: hi tunin,yes there is a sump on the left and the other tank on the right is the r.o. reservoir with auto float top up, the overflow on the top tank is on the left rear ( hard to see couse of the black glass, and yes we have drilled the tank on the right with a ball valve fitted outside the house for 200lts water changes ,the bottom of the tank has also been drilled 4 water outlets driven by sequence 13,000 litres p/h dart pump and another pump (same rate) wich runs the skimmer and another outlet at the top of the tank . i just cant belive how quiet these pumps are !the skimmer is a ev 240 . (rick)