Whether custom or off-the-shelf, every kettle that I have owned has had welded fittings. Sanitary/stainless welders are not that difficult to find. All one has to do is ask around.
I use a 37-degree flare fitting and a flared stainless steel pickup tube that I manufactured on the inside of the 3.5-gallon batch size kettle that I built in the fall of 2013 (started out as a Vollrath Optio 6.75 gallon stockpot). My pickup tube only needs to be finger tight. The advantage of using a flared tube and a 37-degree flare fitting is that the hole in one's false bottom does not need to be much large than the diameter of the pickup tube because the pickup tube goes on the fitting, not in the fitting. Blichmann uses a washer to cover an oval hole in their false bottom because the snap-in pickup tube requires travel.
My custom 6.75-gallon kettle
37-degree stainless flare fitting
Pickup tube installed
Pickup tube and custom Jaybird false bottom installed
False bottom and pickup tube disassembled