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-inch 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-inch up or down movement at every floor level. Four story or more apartment / hotel type buildings need this protection for both concrete and more importantly for wood structures with lots of shrinkage.  

ProVent

www.proventsystems.com