I KNEW it was going to be this video... This isn't pointed at you, but just in general, the title is a bit click-bait-y.

The real takeaway here is to just call it exhaust scavenging and not back pressure. Backpressure is bad, but exhaust scavenging is good. Well, as one goes up, the other goes up, too. Reduce backpressure, and you'll reduce scavenging as well. Increase backpressure, and exhaust scavenging goes up. They're so correlated that differentiating isn't really meaningful in conveying the idea.

They don't go up and down equally; so, yes, there's a sweet spot where you can optimize your ratio of scavenging to backpressure - either through tube diameter or system layout. ...But it's a bit pedantic of a qualification/clarification for casual conversation. I'd argue that's right in line with the content expected from a channel called Engineering Explained, though.

You can change backpressure to exhaust scavenging in the previous comment, and literally nothing is incorrect.