Andy when filling your tank w sump have the return pump/s off. Fill and allow the water to overflow thru your drain into the sump to an inch or from the top of the sump. Turn your pump/s on. The place where the water lines drops to in the sump is the line you can now fill to when the sump is running.
This process ensures that during a power outage your sump will not overflow as the tank drains. Off course you need to make sure your stand pipes are the appropriate length as well.