The home my daughter bought recently does not have any venting for the washing machine, dishwasher or kitchen sink. All are installed in that order from left to right. It is all currently on a 1.5" line below the floor in the crawlspace.
The trap for the washing machine is below the floor and the trap for the sink is above the floor. The dishwasher discharges directly into the sink drain. Soap from the washer backes up into the kitchen sink and it gurgles trying to get air from the sink drain. The sink and dishwasher drain fine.

I have one Studor mini vent for installation now.
Can I use one vent for everything?
Does the vent need to be installed higher than both traps?
What is the best location for the vent placement?

My thinking is to put the the vent in the sink cabinet 4" above the sink trap tied direct into the 1.5" main below before the sink drain tie in.

Hi MM

As I believe you already know, that 1.5" drain is undersized, so at some point I would suggest that you increase the drain size to 2", OK?

In terms of venting I would like to see two studor vents, but you can try installing one under the sink as you suggested. I suspect that you will not see much improvement as I think your drain line may be partially clogged and I think the drain will just back up and close the vent off... *UGH*

It certainly doesn't hurt to try installing the studor vent under the sink. If that fails to resolve issues, then snake the drain and see if that improves things (it should), and if needed, consider installing a new 2" drain line and a studor vent at the sink and at the washing machine... best outcome overall!

Good luck!

Mark

Maintman, where is the home located and are you trying to do this according to code?