Little residential hvac help please. Newer unit leaks water once a year.

EDIT. Just now saw ^^ Dicer's post. DO that. Add a tee and a short standpipe, perhaps 6"

I AM CONFUSED I used to do HVAC /R service and install and DO NOT KNOW what I am looking at

Is this a heat pump? Is this on the return side of the furnace? If it is on the RETURN side, the coil will be under a VACUUM, and the damn thing will attempt to suck water up and keep it up in the pan. (If this is NOT a heat pump and if it IS on the return side, IT DOES NOT BELONG THERE. The coil, that is.)

Anyhow you may be better off WITHOUT a trap at all. What may happen without a trap, is it may gurgle some when running, as it is trying to suck up water and air is blowing past. the water in the piping.