Do I absolutely need a vent if I have a garbage disposal?

Absolutely, a vent is to prevent the trap from losing its seal and allowing sewer gas to enter the home. In parts of the country where weather is extreme, many do not keep windows cracked to allow any fresh air to enter the home so the quality of the air you breathe becomes not healthy.

the water seal of every trap must be protected from being syphoned.
so, yes you need a vent..

A garbage disposer has nothing to do with the need for a vent.

Thank you. My contractor is trying to tell me we don't need one if we have a garbage disposal.

You need a new contractor and a plumbing permit.

actually, because of the disposer's pumping action, a vent would be even more important.

ditto

vent for island sink:


an AAV may be code minimum, but is NOT recommended - do it best practice and be done with it

you need a real plumber, not a 'general hack'

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

Bernabeu, you might need to get a different picture(at least by CA code). It shows what appears to be a sanitary tee on it's back and there's no cleanout in the vertical vent pipe in the wall.

yep

however, it DOES accurately show an 'island loop vent'

(I don't keep these pics, I search each time I need one)

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

I wonder how many plumbers today would plumb an island vent this way - I understand this is called a "Chicago loop" right? I have seen so many islands plumbed with AAV even in new construction which is a shame.

I do have two questions.

When plumbing this way, how high does the loop need to be? Does it need to go all the way to the underside of the countertop? What is the threshold?

Is there a maximum distance between the island and the wall? I ask because if I don't do the loop, but put the same wall vent that branches off from the drain below, it would still vent the sink right? What would be the problem with that unless the line is clogged?

Sum, if you don't do the loop and just take the vent off the underfloor drain, you created an S trap. The loop needs to go as high as possible, no less than bottom of countertop. The horizontal vent length is only limited by the ¼" to the foot rise it needs to have towards the wall.

Thanks steve, I didn't think of the s-trap. I knew there is a reason.

But having that loop there under the countertop it must be a real pain to service the faucet. You have hot and cold supply lines there, possibly a pull out kitchen hose, may be even disposer, dishwasher hose and now a 2" PVC loop all jammed in that space.