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I've got 2 overflows as well. My emergency is just at tank level but threaded a 90 1/4od fitting pointed downward into the stand pipe with a little tubing to get some flow in chamber. Know water not stagnate as pulled out fat fish after MIA for weeks

On main went years without standpipe but since added one and it ends maybe 10" below surface. Only put in to reduce flow back to sump if power fails.

Gate valve directly above sump and it controls the level in the main chamber and easy to adjust from just going over lip to point were main starting to draw air. Keep high though so no waterfall noise.

Strapped all my lines before added water.