Which fitting? Backflow prevention?

Renovating my second-floor hall bath/laundry room. Will be installing a floor drain as extra protection against washing machine leaks and catastrophic failures.

The plan is to tap into the existing washing machine drain pipe. The drain will include a trap primer.

Attached is a rough picture. Blue is framing, red is existing drain line, black is what I plan to add. Questions below the picture.



Three questions:

1. Anything wrong with this approach?
2. What fitting should I use to tap into the existing drain pipe? Wye, tee, or sani-tee?
3. Do I need to worry about backflow prevention? If so, what do you use?

On the backflow prevention point, I have two concerns that I'm not sure are realistic:

- If the drain pipes downstream of this room back up, I don't want dirty water flooding the floor. Eventually, the water will overflow the washing machine standpipe, so not sure if this is a valid concern, but still...
- If the washing machine pumps water out so quickly as to temporarily flood the drain pipe above floor level, I don't want the water to flood the floor.

Thanks for your help!