The bottom of my aquarium will be 18" off the floor and it will have 2 x 1.5" flex PVC drains connected to the bottom of an overflow box, that run into a sump that sits on the floor next to the tank. The sump is 24" tall so the water will actually flow to floor level to the sump then it will have to travel up 6" to dump into the sump. The aquarium is 20" tall if that matters.

My questions are:

1) Will this 6" rise slow down the drainage of the tank even though its still below the water level?

2) If I move the drain to the back of the tank about 8-10" below water level (Thus making the drains all heading downward only) will this help to keep the drainage amount at it's maximum?

The tank will be turning over about 1500 gallons per hour and I cannot have it be slower than this.

Here is a picture to help visualize what I am trying to describe.
http://www.vldesign.com/Untitled-1.jpg

You have a "drip loop" installed in your fish tank. This means the water can drain down no farther then the highest section of the loop. If moving the drains to the back will get rid nof the loop then I'm all for it. If there's still a loop I would either raise the fish tank or lower the filter. Good luck, Tom

Will the loop slow down the drain?

It will slow it down some since the water has to be pushed uphill and the head pressure pushing it is reduced by the height of the loop. In other words, the higher the drain is from the filter the greater the head pressure and the faster the water will drain. Regards, Tom