Stack works fine for me in my UDS and UDG, 2" black pipe, one is a 4" nipple the other just a 4" piece threaded on one end.
I needed a stack because I smoke alot in the rain and am under cover with low sides so I need to get the smoke out. I just put a tin can over the stack to shut the drum down and to keep water or bugs out.
On the UDG the stack is screwed into the bung hole, on the UDS I cut a hole in the middle of the lid and used two conduit nuts for the stack. Here are some pics. The top pic is my first drum and the last pic is the new drum using the flat lid.
Drumhead - UDS x 2 & UDG
Keep on Smokin'
KC native missin' KC
IMBAS Certified MOINK Baller 2009
I also support PETA - People Eating Tasty Animals