50 years ago, I asked Harry Griesback, (if you are really a dedicated plumber, you will know who he was), the same question and he gave the same “assinine” answer. I then asked him to make one of his upside down joints so I could break it apart and see two things. First what happened to the one inch of air that was trapped between the rising lead and the oakum since there was no way to vent it out like there was on a horizontal running joint. And two whether the lead was able to stay hot long enough to completely fill the annular ring, (except for the air). He backed down and admitted that upside down joints were made conventionally first and then inverted. The funnel and running rope answer was a “trade” answer to confuse apprentices, like the steam fitter’s “bucket of steam”.