[quote author=JohnO link=board=DIY;num=1088694760;start=30#39 date=07/27/04 at 15:50:15]Dear Doctor, That was my point exactly Others were saying that the flow rates would automatically match each other. My statement was that they wouldn't and you would need to be able to control one or the other. DX is doing this by the use of a tee section as you mentioned. John [/quote] True, True, but if the overflow was rated @ 750 GPH and you only had a pump that returned 500GPH to the tank, no adjustment would be necessary on either side, return or drain as the overflow will only drain with a surplus in the tank from the return pump. as i said before the 2" partition between the drain pipe area and the outside siphon area prevents the drain from running faster than the pump.