Ambitious laundry project

I have a 4 unit building, and am interested in installing a drain pipe for a laundry in each unit.

The building is arranged 2x2 (2 on top 2 on bottom), with identical/mirrored layouts.

I would like to have the top two units each have a 2 inch pipe, which drains into a 3 inch pipe to run down to the first floor, where it will turn into a 4 inch pipe where two more 2" pipes (first floor) laundries tie in.

The 4 inch pipe would tee into the main waste line, also a 4 inch pipe.

I chatted with a guy at m local plumbing suppl store, he said each laundry drain has to "home run" into the main waste line to be up to code. Sounded like overkill, considering we have buildings with hundreds of units in the city and I doubt every one of them have a 2 inch drain pipe running down to the main sewer.

Is this correct? Also, if my original plan is acceptable, what size should the pipes be as more waste water is fed into them?

i tried drawing a picture in ms paint, but everything came out stupid looking.