The correct answer is option 'A', waste pipe.

Waste Pipe:
The waste pipe in house plumbing is responsible for carrying the discharge from sanitary fittings such as bathrooms, toilets, sinks, and showers to the sewer or septic system. It is an essential component of a plumbing system as it ensures the proper disposal of waste and prevents the accumulation of harmful substances inside the house.

Function:
The waste pipe serves several important functions in a house plumbing system:

1. Discharge of Waste: The main function of the waste pipe is to carry the waste and wastewater from the sanitary fittings to the sewer or septic system. It transports the water, along with any solid or liquid waste, away from the house to a proper disposal location.

2. Preventing Blockages: The waste pipe is designed with an adequate diameter to prevent blockages and ensure a smooth flow of waste. It is crucial to maintain the proper gradient and diameter of the waste pipe to prevent clogs and backups.

3. Ventilation: The waste pipe is also responsible for providing ventilation to the plumbing system. Ventilation pipes allow the release of sewer gases, such as methane and hydrogen sulfide, which can be harmful if trapped inside the house. Vent pipes extend through the roof to allow the escape of these gases and maintain a healthy indoor environment.

4. Prevention of Siphonage: Siphonage occurs when a sudden drop in pressure within the plumbing system causes water to be sucked out of the traps, resulting in the release of foul odors and the entry of sewer gases into the house. The waste pipe includes features such as trap seals and anti-siphonage devices to prevent siphonage and maintain the integrity of the traps.

5. Connection to Sewer or Septic System: The waste pipe is connected to the main sewer line or septic system of the property. It ensures that the waste is properly disposed of in accordance with local regulations and environmental standards.

Conclusion:
In house plumbing, the waste pipe is responsible for carrying the discharge from sanitary fittings to the sewer or septic system. It plays a crucial role in preventing blockages, providing ventilation, and preventing siphonage. The waste pipe is an essential component of a plumbing system and ensures the proper disposal of waste, maintaining a healthy and functional household.