Waste and Water system
No matter how many passengers an aircraft carry, it should have an effective system to manage waste. Toilets and Galleys are the two important areas that require daily maintenance and managing system. In an average a fully loaded commercial aircraft carry 300 to 500 passengers and imagine managing their food and lavatory usage in a long hauls flights. The main constrain in the weight and the airlines have to compromise between the cost and the passenger comfort to maintain a fairly decent waste management system.
Airplanes in early days used to have holding tanks that are usually located immediately under the toilet seat to collect the waste. Then these tanks are lifted out and emptied by cleaning personnel at the airport.
In mid 80’s
Later stages, toilets were flushed with vacuum system that draws all waste into a central tank and emptied at the airport by lavatory service carts.
Newer commercial airplanes
Today newly manufactured aircraft are incorporated with advanced water waste management system that provides a cost effective passenger comfort.
Airplane toilets do not use water to flush, as water-based toilet systems require plumbing that is too bulky for an aircraft, and the motion of the plane could cause water to splash out of the bowl. Instead they use vacuum pressure to suck the waste through narrow pipes into a central holding tank, which is emptied upon landing through an outlet under the fuselage. The vacuum system uses differential pressure at high altitudes and at lower altitude and ground it uses vacuum blower motors for suction. Since the system uses vacuum pressure to flush, it can flush in any direction, including upward and allows the system to work effectively irrespective of aircraft attitude.
As you flush, a very little (0.5litres) water pours into the non-stick coated toilet bowl and wet the waste. Then a heavy suction draws the waste through titanium pipes to the central holding tank in 2 seconds. All the waste will be drained at the airport by lavatory service carts and disposed. It takes 15 to 20 minutes to service the toilet system at the airport. No aircraft will be allowed to takeoff if the toilets are inoperable.
A320 Toilet system