I used a step bit when I drilled the hole for my ball valve in the same pot. I haven't added an electric element but don't see why you couldn't. For my ball valve all I did was use a 1/2" male union 2 female 1/2"unions 2 stainless steel washers and 2 silicone o-rings.
So it looks like this
Female union:Washer-ring:Kettle wall-ring:washer:female union:1/2"nipple:ball valve
The 1/2"male union is in the hole of the pot female unions screwed on both sides sandwiching the washers and oring. Brewed with it over a year now. No leaks or problems. Definately beats trying to siphon wort off the grains.
Good luck happy brewing!!!!