I changed the arrangement of the tanks, and solid filter drain outlet now connected directly to the sump tank, to reuse the water while filtering out the solid waste.
Overview of the arrangement of fish tank, then to solid filter, and then bio filter, and lastly to the sump tank in the ground.
Pipe into the fish tank, with ball valve to control the water flow. It’s about 3 ft. (90 cm) in height.
Pipes to the DWC with ball valve each, and about 16 in. (40 cm) height.
And these are the stand pipes from the DWC back to the sump tank.
All pipe connections are glued, and the connection to the tanks are sealed using silicon sealant. This is far from complete, as I still need to do test run & check for any leaking. Also need to make sure correct water flow from the sump to the fish tank and DWC.