I agree with kenbee's suggestions.

I have a portable dryer of this general type that I built in 1984. It has M/F couplings located on the top, with a petcock at the bottom of the drain. I used it for years as the penultimate step (dessicant/filter on the spray gun) when painting cars out of my rental garage. It was sized to be stood in a 33 gallon garbage can, filled with water and a few bags of ice. I cracked the petcock to drain the condensate... a small stream of bubbles confirmed there was no water accumulating. My design had a single down-leg and three up-legs, resulting in increased heat-exchange surface area and much slower air-velocities leading to the outlet. Even using it "dry", it would drip a nice puddle of water on the floor under it if the day was humid, and, running in ice-water, it must have been very efficient. This setup worked FLAWLESSLY. Never had a drop of water reach my spray-gun. I still loan it out to DIY painters.

I have since evolved, and now have a commercial air-dryer installed in my facility, but have also incorporated several elements of my original old design into the plumbing exiting my dryer. Upstream from the dryer, I have an accumulator tank (20 gallon tank from an old portable compressor) with drain, a 3/4" galvanized, 12' vertical down-leg into a drain trap with purge valve, followed by a 2-1/2" galvanized 12' vertical up-leg leading into the dryer. The air entering my dryer is already mostly dry, as evidenced by the lack of condensate that collects there. Every tap into my building's air system has a trap and drain leg, and every leg from the overhead main exits the main from the top, then 180s to the drop. Each tap is preceded by a quick-connect filter and sediment bowl, and regulator, both with support brackets, as well as a hose support (made from old engine pulleys.) The main is 3/4" galvanized, and has a 3/4" ball valve straight out the termination of the run for blow-out.

My air is clean and DRY.