I used that YouTuber's build to buy my supplies because A) he built closest to Frosty's instructions and he had links to each item so I could order them without having to visit my local HD and deal with the infected. I'm asking for help here because this is where Frosty posted his instructions and there seems to be a wealth of information and here, so I thought this would be the best place to ask about it.
As for the tee, yes it is a 1x1x3/4, per the YouTuber's supplies list.
About the flame going out, yes, the flame seems to either move away from the burner (into the forge) or back up the burner. I'd get a video of it, but I'm starting to get the impression that videos aren't really liked around here.