Rigid PVC exposure to sodium hypochorite

[meatbulbs]

I have an application where I use gray rigid PVC as a drain (manufactured part from rod stock). In the drain I have a threaded hole where a KYNAR fitting screws in where the bleach (>5% concentration at room temp) exits the drain. The PVC threads are, in one instance that I know of, dissolving. In my research I have found that PVC's resistance to sodium hypochorite is rated as excellent. One thing I am trying to find out is how well does it resit the corrosive properties of the sodium hypochorite over time? Is it possible for a drain that has been in service for an extend period of time to lose the battle with sodium hypochorite?