Macerating Toilets vs. Vacuum Marine Toilets Part 2

Macerating Toilets Prevent Odors From Sewage Tank Coming Back Thru Toilet Bowl

All plumbing code for house requires a J trap under the toilet to prevent gases from sewage main to come back thru toilet. Boat building industry has no such requirements.

Vacuum toilets have no water seal. It mostly depends on vacuum (negative pressure) to prevent gases/odors coming back to toilet. In case of vacuum pump being turned off or not working, there is a direct connection between holding tank and toilet without any water seal. There is a valve between hose and toilet bowl and seal on the valve compromised with loss of vacuum.

Macerating toilet, with vented loop has a water seal just like home and seal is reliable even during short term and long term storage.

Low noise

There is a myth that macerating toilets are noisy. Myth has been established by use of rubber impeller in older design macerators. Even macerators to empty out holding tanks and fish boxes use rubber impeller and are noisy.

However almost all manufactures of macerating toilets use centrifugal design for discharge pump. These designs are quieter and make only gurgling sound when runs out of water.

Vacuum toilets are famous for load popping noise. Some customers have described this noise as bullet shooting thru pipe. There are several You Tube videos making fun of vacuum toilet noise on web.

All vacuum toilets and some macerating toilets Marine Toilet require pressurized water for flush water. User should also consider noise generated by diaphragm pump for pressurized water due to toilet system.

Minimum water consumption

It is true that vacuum technique requires less water to evacuate the bowl compared to older style macerator toilets. However water needed to rinse the bowl should also be considered. New control strategies to turn discharge pump and inlet flush water as needed has reduced water consumption in macerating toilets to as low as vacuum toilets.

Minimum power consumption

Power used is measured by amps multiplied by time pump is on.

Vacuum toilet, for example may only draw 6amps. Considering that it runs for 45 seconds, power draw is equal to 6 x 45 =270 amps-sec.

A macerator pump draws 10 amps for 10 seconds. Power draw is 10 x 10 = 100 amps-sec.

Both cases do not consider power required to maintain pressurized water.

Macerator equipped with seawater pump may have a power draw of 18 x 10 = 180 amps-sec, still lower than vacuum toilets.


Vacuum toilet has several components to the system: Toilet, Vacuum generator and holding tank. Components have to be plumbed with leak free joints. There are limitations as to how high vacuum generator can be from the toilet. For boat builders installation requires careful planning. For aftermarket installation a factory certified installer is needed.

Macerator toilets only require installation of one component. Toilet itself is self contained with pumps and control. Only two hoses, discharge and inlet has to be plumbed to toilet. Wiring is also simplified by pre wiring all controls at factory. User only needs to connect to positive and negative at the toilet. Most macerating toilets can be installed by do it yourselfers.


Vacuum toilets function depends on vacuum switch reliability, valve seals, and leaks. Finding a vacuum leak could be a difficult task. Most problems on vacuum system may require a visit from certified technician.

Macerating toilets requires troubleshooting on control. Replacing component of control is easy. Discharge pumps are reliable and seldom needs maintenance.

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Comparison of Macerating Toilets vs. Vacuum Marine Toilets

Macerating Toilets vs. Vacuum Marine Toiltes

There are several beliefs in marine products market about vacuum and Macerating Toilets. Some of these beliefs are true and some are myth.

Let us look at the how both technique satisfy basic toilet engineering functions:

Evacuation of all solids and liquid in one flush:

Vacuum toilet: Stored vacuum is applied to the bowl by opening a valve by paddle or electric. Pressure differential between atmosphere and vacuum pushes water and solids towards the cavity behind the valve. Bowl evacuates quickly in 2 to 3 seconds. As soon as air enters the bowl throat, vacuum drops rapidly. This evacuation technique make a loud noise associated with sudden pressure changes and reduced pipe sizes.

When user closes the valve, suction of the diaphragm vacuum pump is applied to the content of the cavity below valve. Solids and water and air start to move towards pump thru long hose between bowl and pump.

Pressure differential between atmosphere and vacuum accelerate water and solids during initial application of vacuum. Water and air move more rapidly than solids. In order to further accelerate water and solids pipe size is reduced after valve cavity. This sudden change in volume causes more velocity for water and solids and some breakdown of solid from bigger chunk to smaller chunk. After the valve is closed, suction of the vacuum pump moves air and water towards the pump faster than solids. Hence due to lack of positive pressure and water, there is a tendency for solids to splatter on the walls of hose and stay there till next flush.

Once suction of the pump had displaced all the air from hose and valve cavity to builds a preset vacuum level, pumps shuts off. This means pumps continue to run for 45 to 60 seconds after toilet use with typical diaphragm noise. If there is any slight leak in the hose connection or debris caught between valve seat and bowl throat, pump will turn on itself as vacuum drops. This may be an annoying if it happens in the night time.

Due to vacuum, spattered sewage on the hose wall is decomposing under anaerobic environment. Anaerobic odors include a wide range of compounds, most notoriously the reduced sulfur compounds (e.g. hydrogen sulfide, dimethyl sulfide, dimethyl disulfide, and methanethiol), volatile fatty acids, aromatic compounds and amines. Since system is under vacuum, it is unlikely that these odor producing gases escape thru hose. However these odors may be a problem at discharge side of the vacuum pump or during the flush cycle when vacuum level drops to almost zero. Due to notorious sulfur odors, some manufacturers only recommend special odor resistance hose for their vacuum system, increasing cost.

Macerating Toilet: Suction of the pump begins evacuation of bowl. Since pump is normally flooded with water at the beginning of the cycle, suction is powerful and draws solids and water from bowl cavity similar to vacuum toilet without loud popping noise. Most of the Macerating Toilets on the market are centrifugal pumps hence runs much quite than rubber impeller type. There is some gurgling noise similar to house toilets at the end of evacuation.

Suction of the pump is continuous and does not drops as stored vacuum does. Solids are macerated into very fine particles and send thru discharge at much higher velocity than vacuum toilet. Also since particles are smaller and have water as carrier, sewage move further into hose as compared to vacuum

End of the cycle pump stops, noise stops. There is no mysterious running of pump due to leaks or lake of vacuum. Power draw is measure by amps multiply by time. The macerator pump may draw more amps but draws less power compared to vacuum pumps.

Small macerated waste in the hose decomposes in aerobic environment. Aerobic byproducts of gases are odorless co2 and water. This means that a good quality rubber hose is all needed for system, no special odor resistance expensive hose is required.

The macerator pump eliminates waste clog in the hose or holding tank system as well as rinsing of bowl surfaces to remove all stains.

Part 2 of “Comparison of Macerating Toilets vs. Vacuum Marine Toilets” will be coming up soon!

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