Drain and waste disposal is simply transporting the drain water from sinks, baths, etc., and waste from toilets to a through a proper channel. These systems excluding the fixtures and piping are either private such as, cesspool or septic tanks, or they are public sewer systems.
Public sewer systems are not inspected obviously, but the mechanical equipment delivering the waste or drain water to the main waste line from the home is. Private systems can only be inspected on a limited basis because of the buried nature of the system.
It is crucial to know which type of system you have so your inspector can advise you on typical maintenance procedures. One of the key elements looked for when inspecting your waste and drain system is cross connections between this system and your drinking supply water. This can be a serious health hazard and very difficult to find.