I 2nd the powerhead in the sump. What I normally do when I do a water change is to 1st turn off all pumps add a powerhead in the sump keep my reactor and skimmer on and allow them to clean up down below. While this is happening I clean the DT. Scrape glass, rearrange corals/rocks, blow rocks with powerheads and then do my water change. After I do all of this I check the sump and if it still looks dirty I plug in the powerhead and heater and let it sit for a little more.
Thats how I clean my sump.