How long does a 30-gallon black water tank last?

In this blog post, we will answer the following question: How long does a 30-gallon black water tank last? We will explain what a black water tank is, how to empty, clean and disinfect it. 

How long does a 30-gallon black water tank last?

A 30-gallon black water tank can last up to six days. The size of the wastewater tanks (grey and black water) depends on the manufacturer of the caravan and the design of the caravan. 

Manufacturers routinely use tanks with standard measurements, so if at any time you are forced to replace one of your tanks, take precise measurements and you can probably replace it with a higher capacity one. 

RV Make and ModelBlack Water Tank Capacity (gallons)How long it will last (for two people)
Winnebago Micro Minnie254-5 days
Keystone Bullet305-6 days
Winnebago Minnie254-5 days
Dutchmen Aspen Trail28-325-6 days
Jayco Jay Flight32.5-397-10 days

For anyone who wants to spend several days onboard their motor home without being connected to the water, electricity and sewage services of a campsite, they should consider investing in relatively large grey and black water tanks.

It is not unusual for the largest motorhomes to have two grey water tanks, one for the kitchen and the dishwasher and the other for the bathrooms, washer and dryer.

The tanks in a motorhome have great relevance when it comes to balancing the weights on the axles, remember that water is heavy, and a lot. So much so that travelling with full tanks can cause your caravan to exceed its maximum authorized weight.

The grey and black water tanks do not have divisions or baffles inside, these are used in freshwater tanks, these divisions make the movement of water inside a tank significantly less. Full tanks can influence the way your caravan behaves, amplifying its movements. Whenever possible, travel with empty grey water and black water tanks.

What is a black water tank?

The RV’s black water tank is the tank that stores waste. It’s where your toilet water and waste go, and if you don’t have a grey water tank, it’s where all the drain goes.

In RVs, the black water tanks (also known as sewage tanks) are normally located between the upper floor (the one you step on when you enter your caravan) and the lower floor (lower down is just the road).

Besides black water tanks, we also have grey water tanks. Both differentiated from clean water tanks. Gray water is what comes out of a shower and the kitchen, and therefore although it may have soap and some dirt, basically it has not been contaminated with organic remains as if it occurs in the toilet. 

The sewage waters are basically those that come out of the toilet with all that this entails and therefore must be stored, especially if we are in a port, to avoid spillage at the moorings, as unfortunately happens very frequently.

These tanks are usually made of rotomolded plastic, although there are also metallic ones in aluminium or stainless steel. The important thing is that they must be built in inert materials, since they will have to withstand extreme Phs, and thus Nylon and other plastics are very suitable.

The sealing of the inspection opening of the tank must be perfectly airtight because, in addition to holding the exit of liquids, it is essential that they contain the exit of gases, or what is the same, very unpleasant odours.

How to empty a black water tank?

Your water tank should have a drainage system, which will not consist of much more than a tap located at the lowest point of the tank. If access to this tap is not comfortable for you, you should consider placing a pipe and its corresponding tap, in a more accessible place.

If you have to modify your system, take the opportunity to make sure that the drain outlet is placed in the lowest part of the tank and that it allows the complete evacuation of the water contained in it. The bottom of the tank is a better location than a wall.

Freshwater tanks do not usually have slopes that facilitate their emptying, such as faecal or grey water tanks. The bottom is usually flat since the water is extracted by aspiration, through a tube that enters the tank from the top.

Remember that even if you have a simple method to empty the tank, introducing clearly dangerous water, no matter how good a filtration system you have, is a mistake. Above all, it is important to stay away from chemical contamination: pesticides, etc.

As you have read, disinfection, water treatment, filtration, etc. .. are methods aimed at ensuring a trip without health problems. All in all, in my opinion, while travelling in the South of the country in the summer season, you should chlorinate your water tank once a month.

One more tip, if you don’t use your caravan, keep the tanks (not just the drinking water one) empty and dry if possible. Not all tank drainage systems allow their complete emptying, many leave sediment at the bottom, which is still a design problem in my opinion, which should be solved if possible.

What to do if the black water tank fills up?

You do not want to let the black water tank fill up! If this happens, the waste will overflow the toilet and you will have an unpleasant cleaning job to do…

It is important to properly empty, clean and disinfect the sewage tank, and to do it in time. After emptying the black water tank, add a special liquid for the treatment of sewage into the tank. This liquid is responsible for undoing the excrement and preventing it from smelling. 

The amount of liquid you need depends on the brand of the product and is specified on the packaging, for example, 100cc of liquid for every 10 litres of the tank. In other words, if the sewage tank of your caravan has 20 litres, you will have to add 200cc or 100cc but empty it more frequently (when it is halfway up). We recommend emptying it more frequently to avoid the smell of the chemical product.

The bottom line

Now that you know how much a black water tank can last, we recommend emptying, cleaning and disinfecting it as often as possible. Remember that full tanks can influence the way your caravan behaves, amplifying its movements. Whenever possible, travel with empty grey water and black water tanks.

If you have any comments or questions about the content, please let us know!

FAQ How long does a 30-gallon black water tank last?

What is the procedure to treat sewage?

Wastewater treatment begins with the physical separation of large solids (garbage) from their current, using a system of grids (meshes), although such wastes can also be crushed by special equipment; subsequently, a grit is applied (separation of solids)

How to clean the clean water tank of an RV?

To clean the clean water tank of an RV, follow this guideline: to each litre of water, you must add 2 drops of 5% chlorine. If you do, your water will be much more drinkable and clean, eliminating the risk of acquiring different diseases. At we have many years of experience renting and improving your caravan.

Where to dump the sewage?

The sewage is poured directly into an aseptic tank or cassette. The tanks or cassettes that collect the sewage have a rotating tube through which they are discharged into the corresponding drain, and which must be connected to an aseptic pit or the sewer

Where does the grey water come from? 

Gray waters are all those waters that are collected from the bathrooms of the buildings, except for the waters of the toilet. They are collected from the bathtubs, showers or sinks of any building that contains these elements.


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