 all the gas connections for leaks to safely do this. You want to mix a solution of 50% liquid dishwashing soap and water and kind of brush that solution on all of the gas connections and then see if you notice any bubbling. If there are there, that means that connection is leaking and you should fix it before you fire up that grill. It's a lot of work. I'm serious. If you don't stay on top of this and you've got a really big cleaning, it can be a while, but the benefits of it are fantastic and it's going to make that grill last a lot longer.