Plumbers from all states that test their DWV lines need to know about the palmer's™ plug. using knock-out plugs inside a Test Tee plugs is against the code, because part of the knock out plug rim is left in. The Palmer test tee test plug is completely removed. Blow up balls are expensive to plumbers because you have to depend on you apprentice plumbers to take good care of these inflatable balls. Our plastic disposable cup will not get stolen, and will still be holding psi pressure when you return to the drainage waste & vent inspection. Inspectors can fill confident that if a leak results, it is from an unglued PVC or ABS fitting.