In a properly glued fitting, does the pipe actually "bottom out" in the hub? Is there a rule of thumb for how far the pipe goes into the hub? Thanks
It should bottom out when fully inserted.
The cement acts as a nice lubricant when you push them together.
Try to give about a 1/4 turn back and forth to make sure the glue spreads completely as you assemble each joint.
If you push one together hard when dry it will grab and be hard to separate.
You may not be able to get it to bottom out when dry since there is a slight taper on the female side.
The length varies with the pipe diameter.
You can measure a female fitting to the stop (or look up the depth in the manufactures catalog).
Full time plumbers know the numbers by pipe size.