atomrat.com

I went with a 4" Tri-Clamp fitting. I figured that this would allow me to stick my arm into the keg and scrub it out. This also gives a large enough opening to view the inside. The Tri-Clamp also provides an air tight seal. I plan to weld some sort of fitting onto the Tri-Clamp blank for an air-lock, maybe 2 Tri-Clamp with 1" fitting.

I have seen this design by other Homebrewers and Sabco.