Holding Tank

A sealed onboard container designed to temporarily store wastewater, such as sewage or greywater, until it can be properly discharged at a designated facility.

A holding tank is an essential component of a vessel’s waste management system, particularly on boats equipped with toilets (marine heads) or sinks. Its primary purpose is to collect and store wastewater, preventing it from being discharged directly into the waterway, which is often prohibited by environmental regulations. Holding tanks are typically constructed from durable, non-corrosive materials such as plastic or fibreglass to withstand the harsh marine environment and the chemical composition of waste. 

The tank is connected to the marine head or other waste-producing fixtures via a system of hoses and fittings. It is equipped with a vent to release gases generated by decomposing waste, preventing pressure build-up and unpleasant odours. Many holding tanks also have a level indicator to inform the crew when the tank is nearing capacity. 

When the holding tank is full, its contents must be emptied at a pump-out station, which is a facility designed to safely remove and treat the waste. Some vessels may also have a macerator pump, allowing for offshore discharge in compliance with maritime regulations, provided the vessel is in open waters and far from shore. Proper maintenance of the holding tank, including regular cleaning and the use of odour-control treatments, is crucial to ensure its efficient operation and to minimise unpleasant smells onboard.