That means that if ABS and PVC are connected together, some type of adapter or fitting needs to be used. That's it, that's all that's allowed. The image below shows one such adapter on the right side.

Plastics News is showing changes in pricing for PVC, solid polystyrene, polycarbonate, nylons 6 and 6/6, and ABS resins. Low demand sent North American prices for PVC and solid polystyrene resins down ...