While trying to remove the screw in cap to replace some media I broke the reactor in half.  The clear tubing is fairly thin walled and wasn't meant for abuse...so I took it as a opportunity to do some upgrades.  Pictured above is a rubber test cap that attached with a stainless steel hose clamp.  So far its working out, but as you can see by the picure it does buldge while running.

Update:  I have since removed the plasitic test cap as it did pop off one day leaving me with quite a mess.
 

This is a full view showing how I saved some of the clear tubing so I can still see what's happening inside.