I would first get rid of the garden hose. Should be 3/4" pvc. As far as the trap, being an airhandler, it probably pulls air across the evap coil then into the blower, so i would install a trap but Tigerdunes can verify this. Also, your drain should be insulated since it is in the attic.

Hope this helps

Thanks fluffy. Since most air handlers have negative pressure on the drain side I was assuming I need a trap, but wasn't positive. Now I just need to figure out how tall the trap needs to be.. I've read that the manufactured traps aren't deep enough to stop the negative pressure from sucking in water. As far as insulation I hadn't thought of that, what product works best for pvc?

We usually make the traps 5 or 6 " on my 1st drop, 1-2" bottom horozonal, then up 2-3 inches into a 3/4" Tee. Install a short nipple & cap on the top of the Tee. Since most drain pans have 2-3/4" female drain ports, we usually install a place to pour a little clorox & water in one of them and use the other as the primary drain. As far as insulation, we use close cell tubing insulation.

Hope this helps

Fluffy, thanks. One more question - is the purpose of the capped tee for cleanout? The instructions show a plug at the bottom of the trap. What I'm really wondering is do I need to add a vent to the trap? That goes after the trap, correct?

Thanks again for your help. Clearly I'm not a plumber.