Holding Tank Use and Care Guide
Keep our water clean.
- Introduction
- Estimating Tank Capacity
- Avoiding Overfill
- Tank Implosione
- Odor Control
- How much deodorant should I add in my health system to prevent odors?
- Toilet Tissue Issues
- Overboard Discharge
- Dockside Discharge
- Helpful Pump-out Hints
Holding Tank Component Diagram
Introduction
When used and maintained correctly, a holding tank should never interfere with your boating pleasure.
This guide provides you with basic information about holding tank operation and routine maintenance procedures to help you – and the environment – realize the fullest benefit of your holding tank system.
Estimating Tank Capacity
How many flushes will my holding tank hold?
That’s a typical question many boat owners ask about their holding tank. The answer depends on what type of toilet is being used.
But first, you need to know how much waste an adult produces. Field experience shows that, on average, an adult produces a total of 2,6 liters of waste per day, and flushes about five times a day. This means that an adult produces 0,53 liters of waste per flush.
Next, you need to add the amount of water per flush to the waste per flush. The type of toilet you have now becomes important.
A manual or electric toilet can use one gallon 3,8 liters per flush. If you have one of these toilets, the total amount of effluent per flush would total 4,3 liters.
A VacuFlush® toilet, on average, will use only 0,76 liters of water per flush*. This brings the total effluent per flush to 1,29 liters.
Based on this information, you can easily calculate how many flushes a holding tank will hold.
The examples at the top of the next page reflect the capacity for a 75,7 liters holding tank:
* VacuFlush toilets use as little as 0,49 liters of water per flush. Because we recommend adding more water when flushing solids, we conservatively estimate average water use at 0,76 liters per flush.
Estimating Tank Capacity
Manual/Electric Toilet VacuFlush Toilet
Tank capacity 75,7 liters. Tankcapacity 75,7 liters.
Effluent/person/flush ÷ 4,31 liters. Effluent/person/flush ÷ 1,29 liters.
Flushes per tank 17 flushes Flushes per tank 58 flushes
How many days will my holding tank last?
When planning a trip for a number of people, you can now calculate how many days you can travel between pump-outs. Based on a trip with four adults, here’s how long that 75,7 liters tank will last:
Manual/Electric Toilet Vacuflush Toilet
Effluent/person/flush 4,31 liters. Effluent/person/flush 1,29 liters.
Total flushes/day x 20 Total flushes/day x 20
(4 adults x 5 flushes) (4adults x 5 flushes)
Total effluent/day 86,33 liters. Total effluent/day 25,75 liters
Total days to fill tank 0.9 days Total days to fill tank 2.9 days
(75,7 liters capacity ÷ 86,33 liters. (effluent) (75,7 liters capacity ÷ 25,75 liters. (effluent)
The numbers show: a VacuFlush toilet can greatly increase the use of a holding tank between pumping in comparison with other toilet systems manual and electronic.
Avoiding Overfill
While all boats have gauges for the gasoline tank, not all boats have a gauge for the waste holding tank. If your holding tank is not equipped with a level monitor, a SeaLand® TankWatch® Alert System provides an easy way to avoid overfilling the holding tank. 
A glowing red lets you know when to stop using the toilet and pump the tank out.
To monitor the level of holding tank continuously, the Dometic Tank Monitor System features a four-light read-out panel. It shows when the tank is Empty, and when the levels reach Low, Mid and Full.
If you have a VacuFlush or other electric toilet, this system is available with a shut-off relay to stop power to the toilet when the tank is full. This system is available from most SeaLand product dealers and retailers.
Both TankWatch monitor systems are activated by float switches that are easily installed in the holding tank. Simply drill appropriate-size hole(s) (see directions that come with system), adjust probe lengths, and connect wires.
What can happen when an overfill occurs?
If passengers continue to use the toilet system after the holding tank reaches capacity, the contents of the tank will start to flow into the vent line. Because most vent lines are 5/8-inch (16 mm) in diameter, the line will quickly clog. When the tank is finally pumped out, paper and effluent may remain in the line and dry out, creating a solid plug. Since no air can now escape the holding tank, it can become pressurized during subsequent flushes, potentially causing damage to the holding tank or, worse yet, the surrounding boat structure.
If your boat has a vent filter in the vent line, such as the SaniGard™ Vent Filter, overfilling the holding tank can also clog the vent filter. When this happens, the vent filter cannot be cleaned out, and must be replaced with a new one. In short, to avoid the inconvenience and damage that can result from an accidental overfill,
make sure your holding tank is equipped with a “full tank” alert or level monitor system.
Tank Implosion
Too much pump-out suction can be a bad thing.
Today, many pump-out facilities operate at 189 lpm or greater. Without adequate tank venting, the shock of this vacuum pressure on the holding tank and hoses can rupture hose connection points if the control valve is opened quickly. To put it mildly, the resulting mess can be very unpleasant. To prevent tank implosion from occurring, we developed the TankSaver® Relief Valve. It opens automatically when the holding tank is subjected to high levels of vacuum, and otherwise remains sealed regardless of shock or vibrations. And it won’t let malodors escape from the holding tank.
Using a 3-inch (76 mm) hole saw, cut a hole in the top of the holding tank and insert the TankSaver valve. The thickness of the tank walls should be at least 6mm.
Odor Control
Where to find odors, and how to control them.
In a marine sanitation system, there are several potential sources for malodors.
Seawater flushing – If your toilet uses seawater for flushing, microscopic marine organisms which die and decompose inside the incoming water line can cause malodors, especially when the toilet has not been flushed for a long time. Our VacuFlush systems, with freshwater flushing, eliminate this occurrence.
Discharge hose odor permeation – If a discharge hose is installed so that a section may collect standing sewage, anaerobic decomposition of the sewage can begin, and the malodor created by this process can permeate the hose material (rubber hose can be especially vulnerable).
To determine if this is the odor source, use a clean cloth to wipe all suspected areas. Sniff the cloth at frequent intervals. Where molecules of malodor have permeated the hose, the odor will be transferred to the cloth. The offending section of hose will need replaced. If impossible to reposition the hose so it can readily drain, convert the hose to rigid PVC pipe.
Where hose runs are required, SeaLand® OdorSafe® Hose is 16 times more effective against odor permeation than other leading hoses, making it the best choice for sanitation hose.
Ventilation line – Improper installation of a vent line sometimes results in low points that can trap liquid and do not let gases escape. Rerouting the vent hose can eliminate this problem. 
When a toilet is flushed, the effluent entering the holding tank displaces malodorous gases out of the holding tank, through the vent line, and out the through-hull vent fitting. To remove odors before they escape overboard, install a SaniGard™ Vent Filter. The charcoal media absorbs the heavy odor molecules and will last an entire boating.
Deodorants
Effluent in the holding tank and connecting plumbing begins to decompose immediately after entering the system. Sewage decomposition can take place in two ways:
- In aerobic decomposition, bacteria uses free oxygen to digest waste and produce carbon dioxide, water, nitrates, sulfates and phosphates – compounds that do not have offensive odors.
- In anaerobic decomposition, where no oxygen is present, unstable, heavier-than-air, malodorous compounds are produced.
Why use holding tank deodorants?
Deodorants are designed either to inhibit the growth of anaerobic bacteria and stop production of malodorous gases, or to chemically lock onto molecules of malodorous gas and prevent them from escaping.
What types of deodorants are there?
Formaldehyde-based compounds – These are the most effective odor-controlling agents. They are effective over a wide range of temperatures and pH levels, and are also effective in hard water conditions. When handled as directed, the liquid is safe – but the area should be as well ventilated as possible during pouring. The fumes from spilled liquid can irritate the eyes and respiratory tract, so care should be taken in storage (see pg. 16). Switching to a dry, granulated formula would eliminate the potential for spills.
Discharging formaldehyde-treated effluent into a marine environment should not be a problem if the product is used and discharged properly. Formaldehyde is naturally present in the environment as well as through man-made sources.
In water, it rapidly biodegrades, and does not accumulate in aquatic organisms. It is also readily biodegradable in soil, breaking down into water and carbon dioxide.
Preservatives – Preservative compounds have the advantage of low toxicity to humans and the environment, and the disadvantage of less effectiveness and higher cost than typical formaldehyde deodorants.
Quaternary ammonium chloride (QAC) compounds – While QAC’s may not have the pungent odor of formaldehyde-based formulas, they are not as effective in hard or salt water. QAC’s also can lose effectiveness after repeated emptying
of the holding tank without thorough cleaning after each pump-out.
Enzymes – Enzymes are naturally formed as part of a cell’s normal metabolism. Deodorants which use one or a combination of enzymes control odor indirectly by accelerating the digestion of the organic material in the effluent. The main advantage of enzyme-based deodorants is that they are believed to be nontoxic to humans and the marine environment.
How are Dahlberg deodorants formulated?
The liquid deodorant ADINET WC TANK is composed of quaternary ammonium and other alcohols. Our formula controls odors instantly and works and keeps working in the most extreme temperature ranges – from arctic cold to steaming hot. It is manufactured in Spain and its ingredients make it an organic product, adapted to the existing legislation on environmental protection. 
The WC ADINET NAUTIC consists of Biocides, quaternary ammonium wide field of action, surface-active biodegradable and ecologically based Perfume, Perfume odor inhibitor. Available in two-liter bottle, has got level indicator and safety cap, label is translated into four languages. This product is suitable for both freshwater and odorless salt water toilets, as well as portable toilets.
For Grey Water Tank the ideal product is ADINET TANK, because it improves the health of the deposit, and avoids the unpleasant smells caused by soap scum and grease from sinks and showers.
It applies in bathrooms, showers, kitchens, sinks, cabins, floors, etc. It also can be used to treat surfaces caused by the presence of moisture. It is especially recommended for operators and maintenance of health services on board.
How much deodorant should I add in my health system to prevent odors?
Always leave the tank empty as possible. In the case you can not empty the tank, we recommend adding to the tan directly through the inspection cover or through the toilet bowl, 250ml of ADINET WC (Quantity recommended for effective control in tanks of 80 liters). Avoid leaving for extended periods a full tank of waste, because it will cause release of odors and solidify the waste mixed with paper, making the level sensors, fail and give a false reading.
It is important to know that the hose from the toilet can contain debris and waste and it must be kept clean:
1. Flush the toilet for several times to keep the hose line cleaned.
2. Empty the tank through the dockside pump-out facilities or discharge overboard 12 miles off the coast. (never empty the tank in a port or beach)
3. Fill the tank until its water level reaches to ¾.
4. Empty the tank again. (See point 2)
5. Pour 250ml of ADINET WC toilet through the toilet bowl or directly into the tank until next use.
To maintain an odor-free system, pour a small quantity of the product in the toilet after each use.
How can I remove the most standing liquid in the discharge line of my tank?
Flanged diptubes have special angled suction fittings, which reduce the possibility of plugging as occurs with straight diptubes. The angled suction fitting also lowers the tank contents to provide maximum liquid
pumpout. Diptubes permit piping connections to be within the outside dimensions of the tank eliminating space for hose connections in the tank side wall.
Diptubes also eliminate standing liquid in discharge line. Angled “dip tube” allows maximum emptying—will not clog and permits
longer tank shape for greater capacity. Two diptubes can be installed into one tank to provide both.
Toilet Tissue Issues
Most marine toilets flush with very little water (sometimes only ½ liter) as compared to a 6,06 liters, 13,25 liters or 20, 82 liters toilet in most homes.
Many household toilet tissues contain adhesives (for bonding paper fibers together) that may break up well in household systems, but can quickly clog up a low-water-volume marine system.
Do all rapid-dissolving tissues really work?
The ability for toilet tissues to break apart quickly can vary widely from brand to brand.
Dometic Rapid-Dissolving Toilet Tissues, available in double-ply rolls, are routinely tested for rapid-dissolving properties. This toilet paper is made from 100% recycled paper and are biodegradable – resulting in minimal environmental impact as well as outstanding performance.
Do your own “tissue test.”
Put one square of tissue in a glass of water. Slosh it around for five seconds. If the tissue breaks up into many pieces, it will likely work in your marine toilet system. If not, it could cause clogs in discharge lines or “ball up” in holding tanks.
Overboard Discharge
According to Article 24 of the Spill Prevention Act (Order FOM/1144/1999) is prohibited any discharge of sewage from pleasure craft in the following waters where Spain exercises sovereignty, sovereign rights or jurisdiction:
|
AREA |
DISCHARGE OPTION |
| Port waters. Protected areas. Swimming areas |
Not allowed any discharge, even with treatment. |
| Up to 4 miles. |
Treatment is permitted. Solid or discoloration. |
| From 4 miles to 12 miles. |
Comminuted and disinfected is permitted. |
| More than 12 miles. |
Is permitted in any condition. |
Dockside Discharge
When pumping out a holding tank, it is important to create an airtight seal between the deck’s discharge fitting and the dockside suction pump discharge hose. But because deck fittings vary in thread size and internal dimensions, it is sometimes difficult to achieve this seal.
Dockside pump suppliers have tried to solve this problem by using a tapered rubber nozzle that will fit most standard size openings. But the fit is not airtight, so not enough vacuum may be achieved for complete pump-out. And the rubber abrades over time, reducing its effectiveness.
Another remedy was a cam-operated coupling. A special adapter is required for this, and marina-supplied adapters have a strange way of disappearing.
The SeaLand NozAll™ Pump-out Adapter works with both tapered rubber nozzle and cam-operated fittings. There are three NozAll models available to match the most popular deck fitting sizes.
Helpful Pump-out Hints
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Completely unroll the suction hose and lay it with the straightest possible runs to help increase flow.
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Inexpensive plastic or latex gloves should be used. Do not dispose of gloves in water.
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Always wash hands with hot water and soap when finished.
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Clean and disinfect surfaces with typical bathroom cleaner.
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Store hose and attachments after every use. Leave area in clean condition for next boat owner.
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Continually flush pump-out connection with fresh water during pump-out if you cannot make an airtight connection.
