I used a weld-less fitting with an adapter to copper pipe on the inside with a copper elbow, non soldered, and placed it 1/8" off of the bottom and it siphons great. I did not have to flatten the kettle to get a good seal. Check the assembled fitting along the top of the kettle against the curve. The washers are pretty thick and will account for some curve. I measured 3 times and still had to psych my self up before I could bring myself to drill a hole in a one time used 60qt pot. Step drills are great for this.
Primary #1 - Thespian Stout
Primary #2 - Air
Primary #3 - Air
Secondary - Air
Bottled - Wheat Ale, Wee Heavy, The Reverend Clone, Apfelwein