>Share your knowledge without cutting down those with less.
There are many many poor sources of information on the Internet, especially on YouTube. Good production does not mean the content is worth much, or anything. However people like those who responded to me above take what is presented at face value as "correct" which in many cases leads to poor decision-making and poor practices. That may be expensive. In some cases, such as in this video, it leads to accepting life-threatening risk unaware that the risk is being taken.
I can't bear to watch any other videos on the posted YouTube channel so my conclusions are based on that single product. I stand by my assessment that the young couple don't know what they are doing. They are making things up as they go along. They would have been much better off and spent less money cultivating a (perhaps beer-based) relationship with an experienced marine mechanic and asking questions. Or reading any one of several good books on marine diesel engines. Or ask whoever they bought exhaust hose from. Instead, not knowing what they don't know, they dove in spending more time and money than they should have with a result less safe than it could have been.
There comes a point where the best way to share knowledge is to say "don't listen to these people."
Someone posted that this couple has been on boats for ten years. That isn't relevant, especially for people themselves learning (or not) on the fly with no structured instruction. There is a big difference between ten years experience and one year of experience repeated ten times. This is a basic tenet of engineering.
TL;DR: These young people are a hazard to themselves and others.