Replacing washer drain line with 3" PVC - NJ Code

[Winnebago]

Hi all - got some good help on this forum previously from all you nice folks, have another question for my project in NJ.

Wrapping up my DWV for a new attic bath (from this thread) and need to tie into the sewer main in the cellar. Since vertical space is tight on the main stack and there isn't room for another fitting, I would like to replace the current 2" run from the kitchen sink that picks up the washer standpipe (shown in picture #1) with the 3" from the second floor bath, insert a 3x4 sanitee into the stack in the same location, and then tie the existing kitchen and washer into the 3". The kitchen sink appears to be properly vented and has the height to make the connection but the washer drain is a mess (no vent & trap siphons dry on occasion, wye on side, 2" PVC connecting to 1 1/2" CI with a Fernco coupling)

1. What would my new washer standpipe look like and what are the key heights? The whole assembly is about 36" off the floor now.
2. Do I need to further upsize the horizontal run to 4" given that it would be carrying a 3 piece bath, a kitchen sink/DW, and a washing machine?
3. If the local inspector allows an AAV, would it be advisable? What if I wanted to later add a laundry sink with a pump?
4. Is there a way to vent the washer without an AAV here? What would a plumber do?

Thanks for your help.

The stack is just to the right of this image - next to the dryer.



The main goes through the foundation and to street just behind the wood shelf - about 30" off the floor

 

[Terry]

I can't see how far the 4" goes toward the floor, but if it goes into the floor, I would consider installing the 4x3 santee down low. That way you could gravity the washer downstairs.
If the Santee can't be installed low enough, you may need to go with a pump system on the washer. As you already know, not venting the washer with a kitchen sink dumping in from above will siphon a trap. An AAV would help with that.
If you are dropping a 3" down into the basement, you can also drop a vent pipe down for the washer. That would be your permanent fix for the vent. The 3" line would pick up your washer, which is 2"
Lose the rubber Fernco and pick up a shielded coupling that won't allow the shifting of the pipes. Misson and Fernco make those too.

 

[Sponsor]

 

[Winnebago]

If the Santee can't be installed low enough, you may need to go with a pump system on the washer.

The 4" turns just below the hub to go outside (just behind that wood shelf in the picture, so there is no place to insert a T down low unfortunately. I'd be willing to install a laundry sink and pump and let the washer drain into it, how high does the standpipe and trap have to be in this case?

Thanks for the thoughts on venting. I may have enough space to run 1-1/2 up next to the cast iron stack to vent the washer only, or somehow together with my new 3".