My entire house is Plastic. So I can just drain it directly then?So the take away here is that the waste generated by the np is acidic and can cause issues when sitting in a sink or drain.
If you have an older house with metal drain pipes, you'll probably want to steer clear of draining directly into a drain. Modern houses use abs for drains and can handle the acidity.
But another big concern would be the chrome/brass drains at the bottom of sinks, they will definitely get damaged by acid.
There's other concerns as well, what would the acidic waste do when it interacts with the scum inside the drain? What sort of harmful fumes could it produce?
The bottom line is that most hobbyists are ignorant to certain chemical reactions, and it's better for a company to hedge their bets and err on the side of caution to avoid any liability.
If you decide to go directly down the drain, just understand the risks.
I even tear-down my wood walls now fully PVC Walls. Experiences from contaminated my whole house with Rusty Moisture. Even my expensive set of Japan-made Knife that is hanging way on the roof top for BBQ night still get rusted.