There has always been a love/hate affair between engineers and contractors. The impression by many plumbing contractors is that the engineer is an idiot. In a room filled with contractors, you will hear:
I have been on a number of high-rise construction sites where the plumbing contractor just installs the plumbing system in accordance with the plans. When you ask if they understand the design and how everything operates, the answer is typically, “Heck, no, I don't have to. That's the engineer's job. All I have to know is how to install it the way it appears on the plans.”