Wow, just wow!!
I can’t believe after other threads discussing this that ya’ll still get it wrong!!
The primary issue here is that the NG DOES NOT flow OVER the opening to the “leg” to deposit any debris or moisture. IMO, there are two methods to correct this set-up.
- move the leg to the other side of the Tee (where it should be),
or - increase the slope of the horizontal run (to furnace) to at least a 45 degree angle (redneck fix).
The current set-up would only possibly work if the NG was under a high velocity to ‘throw’ any debris/moisture past the Tee!