AC Drain line

Im asking for a freind. He recently had an AC system installed, and when they did the drain line, they basically just put a TEE on the end of the AC drain line and set it in the vertical piece that goes to the trap and into the vent. Well, since its sort of 'open' where they laid the tee, crap got in the trap, it backed up and dripped into the attic and cieling. So, my question is, when they install these, they are supposed to be completely closed right? Like with glue and everything so that if it backs up, it backs up in the pan and then leaks out the secondary pipe indicating a problem.

 

I have the same situation, but they tee'd into a copper vent pipe for both the AC and heater. Lasted about 11 years before it eat out the copper and we were wondering where the water was from.

You will find whether AC and or heater lines, they have to be kept clean regardless where they are located. Just make the effort to flush them every couple of years. A good water detector is also good insurance.