Aggie,
What's that yellow tube, output back to your main tank? The easiest way is to tee off your input tube with a ball valve so that the bulk of the water goes into your sump and a small amount goes to your refugium. With the refugium slightly higher than the sump, the water will flow into the sump without using any electric pump. You just need to use a bulkhead in the refugium for the output. If that yellow tube is your input tube, then it might be hard to tee it off.