Washer to old drain

Hey guys,

I'm new to this thread but I am completely stumped with this project. There are a few things i am unsure of.

I am looking to install a washer into this 3" cast iron stack that is running out of my basement, it is unvented but down the road i plan on running a work around vent to the roof for it. For now I am wondering if it is able to have an auto vent in place as shown in my diagram. I would run it higher than the minimum needed above the p-trap. This isn't the part where I am unsure. The cast iron drain(3") seems to have a p-trap at its bottom. which would obviously be unvented due to it being, ya know, in my floor. This is what a plumber I had come in say his plan would be, whether or not he noticed the second p-trap, im not sure. Would this work? Code aside.

First of all, you won't get any "code aside" advice here. The purpose of this forum is to offer advice to DIYers on how to accomplish their plumbing tasks code legal. Second, the trap you show in the photo is not a P trap. It is an illegal S trap. To be a P trap, there would need to be a vent basically where the high point in the trap is. That is, before the drain makes the downward bend. I think you can use an AAV as you describe, but the S trap has to go.

Thanks for the quick reply, your right, i should have known id get "proper" advice here haha. I am not familiar with S traps as im sure they were done away with on purpose. What would end up happening if I drained into this? just wondering if it can be left until I can get a chipper to replace it to a 90deg turn.

Work around?

Could I even cut this off at the floor and add something to run straight from this spot?
bypassing the rest of the cast iron altogether.

If you tap out a little concrete, you may find a hub fitting that you can insert the new pipe into.

The you can add the vent, trap arm and p-trap with standpipe.