Aquaclear overflow to refuge

Well, your plan is not without merit. I think it can work if you know what you are doing and don't mind cutting into a perfectly good AC filter.

But if you want to pump water out of your tank and into a sump, there are easier ways to go about it.

If you want to pump water out of the tank, rather than cutting into an AC filter and risking destroying it, you might be better off running a length of tubing from the output of a powerhead. Place the powerhead in your tank and it will pump water from your tank, through the tubing, and into your rubbermaid sump.

There is a possible flaw to your design, however. You are just using an ordinary powerhead to pump the water back into your tank? You will need a pretty good powerhead to pump the water from your sump back up into your tank. You might be pushing around 4 or 5 feet of water. That is heavy head of water to be pushing upwards against gravity. If your powerhead stops working for some reason (which some powerheads have been known to do), water will continue to flow into your sump until half your tank water is all over the floor. You will probably need to buy a water pump, especially designed for the purpose of pushing water back into your tank at the proper rate.

Secondly, it's important that the water flow remains constant in both directions, to and from the tank. Will you have media in the AC? Are you going to pre-filter the AC? The reason I ask is: if the AC becomes clogged, or if the pre-filter becomes clogged with mulm, the results could be disasterous.

Hope that helps and good luck!