That drain plug on the right rear underside of the engine is used to indicate what? Sumping ? I removed that plug years ago just because. Nothing drained out. Engine was stock 96 Cu in at the time. This afternoon I decided to have another go. Oops. Drained off about 1/2 pint of engine oil. Not burnt or smelly though. If this an indication of sumping, explain the oil path that allows the oil to get there. Or am I completely wrong on this being an indication of sumping. The engine has been upped to 107 Cu in with my mechanical prowess and although I'm well attuned to the engines characteristics, I've never felt any bogged down indicators typical of sumping. The 2010 FatBoyLo service manual was of no help. One pic shows the drain plug. Makes no mention of function or why it's there. Thought maybe one of you well versed Twin Cam wrenchers could school me on this. Thanks

 

That is a sump plug. Removing it usually isn't reccomended as replacing it usually involves a cracked case.
Having a few ounces of oil drain out is normal from what I've seen in here.
Sumping in a TC usually involves a Softail with the elevated oil tank and a bad seal, o-ring, or something else that allows the oil to drain from the tank into the crankcase after the bike has sat for a while.

 

Thanks QC. I knew about the "no tamper" aspect of the plug. Never seize and a light tightening going back in. I'll have to monitor over the winter lay up to see if the oil tank drains down and oil reappears at that plug.