Is it proper to set up the kitchen sink behind the toilet like so in the diagram below?



What are the alternate ways of connecting the kitchen sink. Could you connect it to the tub/lav horizontal drain pipe if it were 3"?

vertical vent venting allowed but you must increase the pipe size in the vertical wet vent. Normal KS drain of 2" should be increased in one pipe size to 2 1/2. But unlikely this will ever happen.

move the kitchen drain to downstream of the 3 x 2 Y that catches the lav and tub.
the toilet is wet vented thru that 2" pipe so it needs nothing else.

quote; Normal KS drain of 2" should be increased in one pipe size to 2 1/2.

You must be an engineer who goes by "tables" rather than reality. WHERE would you find ANY "two and one half inch" drain/vent pipe or fittings? It is like the engineers who calculate vent sizes and decide it should be 3 1/2" even though it is impossible to find it.

Doug, how come a 2 1/2 pipe for the vertical KS drain/vent pipe would be required?

Packy, is the below what you mean about moving the kitchen drain downstream the lav/tub 3x2 Y?

absolutely perfect..