Originally Posted by david_42
Because the kettle is a cylinder and the washers are flat, you need a compressible seal on both sides.
I'd disagree. One o-ring on the inside is enough, thats how mine is all plumbed up with zero problems. An oring on the outside and inside actually allows the fitting to move more which may cause a leak to form sooner. The nut seals the threads and the o-ring and jam nut prevents liquid from leaking through the opening around the fitting. The internal pressure from the water column helps makes this seal even tighter.
Save the second one for a spare