The half inch PVC line to cover the bottom of the bag is probably to make sure that the plumbing is always at the bottom of the bag and not floating around in there so it always drains completely. This way once the bag is empty the hard tank will start draining so you don't need to T the line, they will fill and drain one after the other using the overflow that is already present. You just have to add another vent/overflow to the bag. (Message edited by jtnz on April 21, 2008)
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