Onboard toilets: The advantages and disadvantages of each system

Onboard toilets are an indispensable part of a boat's equipment and crucial for well-being on the high seas. Toilets that are complicated to use or leak can significantly reduce the satisfaction of boating. Not only are the odors unpleasant in some circumstances, but there is also the risk of not being able to use the toilet at all. Laymen often believe the myth that with marine toilets, human metabolic products flow directly into the sea after flushing. Of course, this is not always the case. Rather, there are numerous types of on-board toilets available today, all of which offer different advantages and disadvantages. Here you can learn all about the different types of seawater toilets and how to use each.

What are on-board toilets?

An on-board toilet describes the sanitary facility on board vehicles such as ships, aircraft, caravans or coaches. The first systems were open and discharged feces directly into the environment. With increasing environmental awareness, the open variants were replaced by closed systems so that targeted disposal is ensured.

How do on-board toilets work?

The toilet is flushed with either sea or potable water: a hand or electric pump can be used to pump the water into the bowl. The same pump is then used to pump out the feces (either into a holding tank or outboard). The pump has a dual function: on one side it empties excreta and on the other side it acts as a flush with water for cleaning.

What are the types of on-board toilets?

The standard on most boats includes either the mechanical on-board toilet or the electric on-board toilet. Since the handling of the two forms differs, the use of the boat toilets must be explained and / or before the start of the trip.


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Mechanical on-board toilet

The manual on-board toilet does not have a conventional flush like the toilet in your home. On the side of the on-board toilet there is a switch for pumping, another switch for flushing and a pump lever. 


In order for the human feces to be pumped out, one flips the switch for pumping out and simultaneously operates the pump lever. By flipping the lever, the entire contents of the toilet are pumped out. 

With the lever you can run water at the same time to flush down the feces. If you want to pump the toilet bowl empty afterwards, you should set the switch back to "pump down" and manually refill it five times. After the pump lever is locked, the on-board toilet is ready for the next operation.

Electric on-board toilet

An electric on-board toilet works in a similar way to a manual seawater toilet. The difference lies in the handling: Instead of the manual hand pump, the electric system takes over the pumping. Therefore, the electric marine toilet does not have a pump lever, but only two switches for pumping and flushing. In the field of electric toilets for sailors, there are various models that differ in their comfort.

1) Entry level models 

Electric marine toilets are available, for example, as entry-level models with submersible pumps. The on-board toilets with chopper have both chopper and impeller pumps integrated.


2) Household style electric on-board toilet

In addition, there are electronic on-board toilets of household design, so that the pump is already installed in the porcelain bowl. At the same time there is the possibility of additional insulation. In this form of electric toilet water and energy consumption depends on the flushing time. This is determined by the duration of operation of the flush button.


3) Electric on-board toilets in modern designs. 

The latest models of electric on-board toilets have large choppers with a diameter of 80 to 120 millimeters and a quiet motor. The noise level is comparable to that of a standard household toilet. Water consumption ranges from 1.5 to three liters per flush. In addition, most models can be used in conjunction with a holding tank without any problems.

Chemical toilets

In addition to the described models, you can also opt for chemical toilets, which are considered the ideal solution for small boats with limited space. The small on-board toilets take up little space and do not require a power supply or an external water or waste tank. However, the chemical toilet is only recommended for short trips, as the capacity is limited.

What are the advantages and disadvantages of each on-board toilet?

Each on-board toilet comes with different advantages and disadvantages.

Advantages and disadvantages of manual on-board toile

One advantage of the mechanical on-board toilet, in addition to its without electricity, is its quiet noise leveluse. In addition, manual on-board toilets are inexpensive both to purchase and in terms of running costs. Consumers thus save on electricity and replacement parts. If the boat toilets do not require maintenance, they demonstrate high operational reliability.

A disadvantage is that the use of the manual on-board toilet requires explanation. This can cause problems, especially with children. In addition, water consumption is uncontrollable: Many people pump too much or flush too much water, so that the tank is quickly full. The seals and valves also need regular maintenance. Lastly, the toilet tends to clog quickly.

Advantages and disadvantages of electric on-board toilets

The biggest advantage of the electric on-board toilet is probably the ease of use: There is no need for the time-consuming pumping of a mechanical boat toilet, so that no more water is pumped than is needed. Thus, a controlled water consumption can be ensured with each toilet flush.

However, there are also disadvantages with electric on-board toilets: On the one hand, use is associated with high power consumption and, on the other, the pump is quite loud. The noise generated by the chopper and impeller pumps can be very extreme in some cases and is particularly annoying when used at night. The purchase price is significantly higher than for a manual toilet on board.

What do you need to consider when disposing of wastewater at sea?

The International Convention for the Prevention of Pollution from Ships (MARPOL) regulates the discharge of ship sewage. As a result, the discharge of wastewater from ships is prohibited in principle. Accordingly, wastewater and fecal matter must be collected in a wastewater tank or fecal matter tank and disposed of in the port or via special fecal matter suction systems.


Every mariner should read the relevant laws and regulations before sailing. In areas where discharge of ship sewage is permitted (regardless of distance from the coast), disposal must be done at a sailing speed of at least 4 knots. Those wishing to make excursions along the coast should dispose of the ship's sewage in the harbor using the fecal disposal system provided for this purpose.


How to empty the on-board toilet?

The on-board toilet can be disposed of either at a special port station or at sea (far from the 3-mile zone). Emptying at a harbor pump station may be subject to a fee. The service provider connects the boat to a suction device and takes care of the treatment as well as disposal of the wastewater.

Emptying at sea depends on the position of the toilets and holding tank in relation to the waterline:

  • Below the waterline, the use requires a lye pump to evacuate the water through the board passage
  • For on-board toilets above the waterline and the tank below the same, a drain pump is required
  • If the tank is horizontal, a pump must be used to evacuate the wastewater
  • If the tank is vertical and 50 centimeters above the waterline, it can be emptied by gravity

What to look for when using the on-board toilet?

Regardless of whether you choose a manual or electric on-board toilet, you should flush with potable water to avoid excessive odor. If you don't do this, flush with a seawater pump so that water is pulled up from the sea and made available for flushing. You can clearly notice the difference between salt and fresh water. Therefore, you should trust their sense of smell and choose a variant with drinking water.


Onboard toilets can quickly become clogged. Therefore, you should never throw anything other than toilet paper into the on-board toilet. In addition, do not use too much paper. Alternatively, you can throw this in the trash can to prevent necessary repairs.

To empty the waste tank, a waste pump on board is suitable. Here you should pay attention to the required delivery head and power.

What are the most common mistakes when using on-board toilets?

The most common mistakes made when using on-board toilets are:

  • The lever was not flipped
  • Too much paper is used
  • Garbage or hygiene products end up in the toilet
  • Too frequent pumping or rinsing
  • Sharp WC cleaners that can damage the pump
  • Salt water is used for rinsing


What are the different names for on-board toilets?

On-board toilets are also known as "water closets", "seawater toilets" or "boat toilets".

What must not be disposed of in on-board toilets?

Only faeces and toilet paper are allowed in the on-board toilets. Rubbish or hygiene articles have no place in the on-board toilets.