ProVent’s New EZ Mechanical Coupling is a flexible rubber expansion joint made specifically for PVC DWV plumbing stacks. Stacks require at least a 1/2" movement at every other floor to protect the PVC branch piping from possible breakage. This tested inexpensive expansion coupling will compensate up to 3/4" up or down movement at every floor level. Four-story or more apartment- and hotel-type buildings need this protection for both concrete and, more importantly, for wood structures with lots of shrinkage.  

proventsystems.com