To most people the building drainage system, lying below the beautiful and pristine (pure) ceramic (floors) and stainless steel appliances presents a mystery beyond their usual knowledge. How does the water used in kitchens, bathrooms, wash basins, water closets disappears quickly is of little or no interest to the users. The users become cautious and concern only when either they are faced with a foul smell somewhere down there or are met by a filling WC bowl which keeps on filling and pours on the floor creating filthy conditions. The mystery surrounding the drainage system suddenly depends on receipt of costly repair bill.
In fact, there are few mysteries about the operation of a building drainage system ...