Okay, great!
Assuming the gate valve I circled in blue is on the primary drain (aka siphon channel, has shortest standpipe), here’s what to do:
— With the full tank/sump circulation system operating, start by opening the red gate valve all the way until it stops by rotating counter-clockwise… this will make the system very noisy as air is sucked down the drain and into the sump with the water…
— Start by closing the gate valve a quarter turn clockwise at a time, waiting at least 30 seconds between turns… you will likely go several full turns before it restricts the drain enough to start actually tuning it in…
— you’ll go by sight, sound, and touch here; seeing bubbles discharging in the sump, hearing bubbling/gurgling, and feeling the valve you’re turning vibrate as air bubbles pass through it…
— continue closing the gate valve 1/4 turn at a time, once the bubbles discharging/water gurgling/vibration through the valve start to reduce, or become intermittent; you know you’re getting close… now it’s time for “fine tuning” smaller increment adjustments, and waiting 2-3mins between adjustments!
— once tuned, the primary drain plumbing will stop discharging bubbles, the vibration through the valve will be gone, and the tank will run silent!
— you know you’ve closed the primary drain too far if the secondary drain (aka open channel) starts draining more than a trickle, or discharges bubbles/gurgles!
— remember, wait a few mins between any valve adjustments during fine tuning; this gives any air still trapped in the plumbing/standpipe time to escape!
The idea here is to restrict the primary drain just enough that it can’t suck any air in with the water, creating a full siphon, and silent operation! — if operation is silent followed by intermittent moments of gurgling; the siphon is starting and stopping! (Fine tune valve again in this scenario)