A licensed plumber is not required everywhere. I do all the plumbing, electric, engineering, etc for our home, farm buildings and our USDA inspected meat processing facility (a.k.a. butcher shop) which I designed and built for our farm. There are typically exemptions for non-public buildings in many locals. Read the regulations and laws. Read the code - I still follow code even though I'm not required to do so and I also involve the state plumbing, electrical and other inspectors which they appreciate although before they set foot in the building they give the obligatory speech that they do not regulate us since we're not required to be regulated by them. Still, they're a wealth of information.
That said, what I do is rather than putting every little detail into the drawings I rather indicate plumbing, wiring (all conduited), water, gas and other lines with simple paths. This is simpler and then the plumber (me), electrician (me), gas installer (me), etc will know where things are meant to go and do the final details. I do specify slopes. I do conduit, trench and channel everything as I like things hidden away in the walls, ceilings and floors. Since I built to and beyond USDA specifications for our butcher shop (and use the same techniques for our home) and I'm the one who does the cleaning after each butchery day I want things to be as easy to clean, as easy to maintain and as long lasting as possible. Reducing my maintenance leaves me more time to do research and construction of new things.
