Can I drain a vanity between washer standpipe and toilet?

[JimmyJoeJohn]

I'm in the midst of remodeling a second bath and I'd like to add a sink vanity. The current toilet stack already has the washing machine standpipe connected to it.

I don't think tying above with an upside down sanitary tee will be an issue for venting but my question is if I can splice a sanitary T between the washing machine standpipe T and the stack going to the toilet drain to be able to drain the sink.

I've attached a crude picture trying to show what I mean. I'd be adding the bits in green. (Horizontal sections would have 1/4" per ft slope)

Is this allowed? Will there be any issues with this setup? Would it be better to put the sink drain above or below the washing machine T?

 

[Mzeb]

This is how I've been looking at plumbing our new half bath that shares a wall with our new laundry room. What I think I've read is the washer can't be upstream of the toilet or the toilet may gurgle or water level rise/fall. Do you have any issues with the current setup? I hope someone will answer your question.