Weldless and o-ring Location

I was wondering what everyone is doing with their O-rings on their weldless bulkheads, thermometers, etc. I have seen so many conflicting reccomendations on them being inside the vessel or being on the outside. I assume that either way will probably work fine, but has anyone had a bad experience?

Mine are on the inside and outside.

I just converted a keg into a BK for my brother in law. I used the kit from Stainless Brewing.
It’s a nipple, two silicon O-rings, and two nuts.

They have great prices, and it came in three days.

Outside on mine. One thing you can do to make a better seal is to cut a 3/4" hole instead of 7/8" and then used a knurled bit to gently open the hole just enough to slide the fitting through.

Outside on mine too. Isn’t there a slot for the o-ring on the flat of the valve? That holds it in so it won’t squeeze out. Mine stay sealed even though I pivot them occasionally to raise/lower the level of the pickup tube. Great products.