I currently have a kitchen sink on the first floor which leads to a vertical pipe (illustrated in black). I would like to connect a bathroom sink to the same vertical pipe (illustrated in orange). Can I do this using a 90 degree tee or does both pipes have to be connected separately to the vertical pipe?
For reduced clearance, use a "double wye" or a "double fixture fitting" and cap off the vertical (the opening at the top).
You need the sweep for the clean-out and to prevent water crossing over or inhibiting flow when both sinks in use.