1) fill DT untill water flows over the overflows and into the sump untill return pump has enough water to start the water cycle into the tank and back into the sump withought much air being sucked up by the pump.
2) turn on return pump for about 2-5 seconds to get water returning to the DT.
3) let the system back siphon and wait for it to stop draining back to sump and make a mental note on where the water line in the sump is at this point.
4) Turn the return pump back on and let it start pumping the water back over the overflows into the sump again.
5) again turn of the return pump and let the system back siphon fully again and see if it fills to where it did the 1st time. (if not. continue to do steps 4-5 until you have an average water height)
6) turn the system on fully and add water to the sump until you have no issues of the return pump sucking in air.
at this point you'll know your absolute minimum water level with the system running. I usually mark my sump 1/2-1 inch above this point.
7) turn the return pump off and let the system back siphon 1 more time.
8) fill sump to the highest you ever want it to be.
9) turn the return pump back on and wait a few minutes for the system to level out any surging
10) mark your waterline in the sump as max water level so you'll never put more than the system can handle into the sump on accident
11) sit back and enjoy your new sump'd TD
Hope this helps,
Casey