Vacuum toilets are the most effective type of toilet system for preventing pollution from ship waste. They are designed to collect sewage in a sealed tank, emptying it at a shore-based facility; this ensures no direct sewage discharge into the marine environment.

Cruise ships use vacuum toilets primarily to conserve water and save space, which are critical commodities at sea. A standard gravity toilet uses about 1.6 gallons (6 liters) of water per flush, whereas a vacuum toilet uses only about one-quarter of a gallon (1 liter). On a ship with 5,000 passengers, this saves millions of gallons of water per week, significantly reducing the energy needed for desalination and the weight of the wastewater being hauled. Furthermore, vacuum systems do not rely on gravity, meaning the pipes can be smaller and routed horizontally or even upward, allowing for more flexible cabin layouts and thinner "deck" spaces. The "whoosh" sound you hear is the result of the immense pressure differential that pulls waste through the system at over 100 miles per hour, which also makes the pipes less prone to clogs compared to traditional plumbing. It is a highly efficient, closed-loop engineering marvel that keeps the ship sanitary and environmentally compliant.