A vacuum collection system is a conveyance technology that utilizes pressure differences and is widely used in aircraft and high-speed railway vehicles.
In the marine sector, these systems are also increasingly being adopted as an efficient means of handling wastewater within limited spaces.
This article explains the system’s main components and operating principles.

1.1 Main Components of a Marine Vacuum Toilet System

A vacuum collection system primarily consists of the following three elements.

Appliances
These include toilets and urinals that discharge human waste (sewage: blackwater), as well as washbasins, sinks, showers, and other fixtures that discharge wastewater (greywater).

Piping
The piping maintains the vacuum throughout the system and conveys the wastewater.

Collection / Generation Units
These units form the core of the system and perform the following functions.

　・Vacuum generation: Vacuum pumps continuously maintain negative pressure within the piping.
　・Collection: Conveyed blackwater and greywater are temporarily stored.

1.2 Wastewater Conveyance Mechanism

The vacuum generation unit maintains a vacuum (low-pressure condition) within the piping.
When the toilet flush button is activated, atmospheric air (high pressure) rapidly flows into the piping.
The resulting high-velocity airflow, generated by this pressure difference, physically pulls the wastewater through the piping.

Normally, wastewater is conveyed approximately 10 to 20 metres with each flushing operation.
As subsequent flushing operations are repeated, the wastewater moves through the piping in stages and eventually reaches the collection unit.

1.3 The Heart of the System: Vacuum Tank

A vacuum tank is commonly used within the collection and generation unit, which serves as the heart of the system.
It primarily consists of the following three elements, enabling continuous wastewater treatment.

Vacuum Pump
Maintains negative pressure within the piping and draws wastewater into the unit.

Buffer Tank
Temporarily stores the wastewater drawn into the unit.

Discharge Pump
Forcibly transfers wastewater accumulated in the tank to the ship’s sewage treatment plant (STP), a holding tank, or a public sewer system ashore.

※Some manufacturers use integrated pump units that combine vacuum generation and discharge functions, allowing direct connection to treatment equipment without an intermediate tank.

About This Article

Reference
・Evac Group, “Vacuum Collection”,
(Last accessed: February 23, 2026)

※This article was prepared with reference to the source listed above and organized based on the author’s understanding.