Adding a Laundry Sink to Existing Washer Drain

I posted this question at the end of a very old thread (https://terrylove.com/forums/showthread.php?17967-utility-sink-drain&p=277172&highlight=#post277172) and didn't receive a response, I have an existing standpipe for my washing machine going into a 2" drain vented above with 2". The washing machine drain comes from the left in my picture.



I would like to add a laundry sink to this drain. My question is Washington Code specific as I live in Washington. Can I simply add a cross T where the washing machine enters this stack and drain both the sink and washer at the same height, or do I need to do a vent in the horizontal line come from the sink trap just as you have shown in the picture at the beginning of this thread?

You can use a fixture cross at the same height and use the one vent.

Not a san cross. What you have now is a SanTee.
A double santee wouldn't work. I would need a double fixture fitting.

Offhand, from the pictures, I would suspect that a fixture fitting would make the drain go in the wrong direction and create a convoluted drain if the sink is going along the back, concrete, wall.

So I went to Home Depot and found these two fittings. It appears to me that I need a double fixture fitting, shown on the left. Is this correct? if I replace the T that I have right now with a double fixture fitting I won't need to change the vent at all?

Yes, the box on the left. If you need to get closer to the wall, you can offset below the fixture tee.

Terry said:

Yes, the box on the left. If you need to get closer to the wall, you can offset below the fixture tee.

Click to expand...

Hey Terry, that looks like a double combine, not a double fixture fitting?