7. Building waste
No matter where the building waste came from, you should never throw it down the drain. This goes for both very small pieces and even powder-like debris. Big chunks form clogs and the small ones can end up on the sides of the drain and lead to even more serious problems.
They might seem completely innocent at first, but you should keep in mind that they are made of latex which never dissolves. They can also stretch very well and get stuck inside pipes. Besides, condoms can get filled with air, water, or other waste which will lead to a very serious clog that could be very hard to get rid of.