It can take very little to cause a major blockage. See the pipes article in my cave.
A "simple" dent in the pipe isn't usually a problem unless it's fairly deep.
The problem is when you see a pipe dented/bent between the rear support bracket and the large bends heading up to the engine. Most often between the bracket and drain. What looks like a slight bend from the bottom frequently hides a major crimp on the top that can easily block half the diameter or more.
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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurasic Park)
The Ogre's Fiero Cave (It's also at the top of every forum page...)
