Fixing an Illegal S Trap with In Line Vent AAV and P Trap 

This is the wrong way to install a vent the vent should terminate 13 inches above the flood level of the sink.This information is from a master plumber

Not a lot of space above the vent to unscrew if you ever needed to replace the unit from what I could see in the video.

Don’t take the distance-above the Tee as being gospel. Check your local codes to ensure that distance above is above-flood or above-tee. You will fail inspection and could have problems filing insurance damage claims for overflow flooding if not done properly.

When was the original installed??.. if before no S traps allowed -it is legal. No code ever says to go back and update any system installed under a prior code or no code. You only have to meet the current code on anything installed at that time.

Very helpful thanks. If one instead used an open external vent pipe, what's the minimum height it needs to run to please?

It can every where else in the world America must have different water to rest of us

Wait a minute? You're advocating this is a fix? Looks like you're doing a pretty extensive rehab. You have the walls open seems you're in the basement as the pipe terminates to concrete so you have access to this vent, but failed to connect to it through any and all means. You're leaving the ferco tee which appears to be inside of wall. where is this 4 inches that you mentioned coming from at least 4 inches? you need to be 12 inches above the rim of the flood zone? Which in your case is top of your washing machine trap arm which absolutely needs to be 2 inch in size you will not like the results of leaving that vent in that location where you're clearly draining the washing machine above the point of vent… your washing machine is going to discharging! Out of your vent!!!!….. DoDYI

When you say "illegal", do you mean illegal in CA?

It's not illegal.... The vent must be 6" above sink!!