(Cracks knuckles...let’s do this)
If your drain is pushing out bubbles, it isn’t siphoning and most likely your secondary drain is handling the bulk of the flow. Since it has a hole on top for the airline tube, it’s able to pull air into the drain, hence the “hottub” effect. How I remedy this and put the flow where it should be is to remove the durso altogether from the primary drain. It’s unnecessary. The problem with running durso on the primary full-siphon is that the water level in the dry-side of the overflow box needs to be high enough to create a pressure differential that’s great enough to force the trapped air bubbles in the tube out of the bottom and into the sump. By removing that durso, you lower the necessary water level to get the siphon started efficiently. That’ll fix most of your problem. Tuning should be a matter of closing the primary drain’s ball valve until the water level in the dry-side overflow very slowly creeps up to where the secondary drain starts functioning. Technically, you don’t even need a ball valve for the secondary drain, but I use one and ever-so-slightly close it just to reduce noise more than anything.
this would work great IF he had a secondary drain. However, he only has a single, durso, drain.your main drain the one with the two 90 on top is supposed to be under water bout half way down the overflow with a gate valve on it.
second pipe sou;ld have two 90s on it at the level you want water in overflow, i suggest up near the top because water going into overflow makes noise in itself.
doesnt look like you have another hole for a emergency drain.
you adjust gate valve to where bubbles stop coming out main drain or you can tweak it a bit allowing some bubbles but not enough to make much noise and the other pipe will automatically set the level in you overflow and handle the rest of the flow.
i have 2500 gallons a hour going thru mine and its whisper quiet.