How Often To Dump Black Tank?

Having a toilet on board is one of the (many) advantages of RV camping over tent camping. There’s no need to line up to use sometimes questionable public facilities at a campsite, wait until you can find a gas station bathroom or, in extreme situations, head off into the woods.

An RV’s onboard facilities are plumbed into a black water tank, and improper maintenance of that can quickly turn a great trip into a stinky nightmare. But how often should you empty your black water tank to avoid this?

Ideally, a black water tank should be emptied, at the very least, at the end of every camping trip, and some say every three to five days is a better rule of thumb, or when it is ⅔ full.

In reality, just how often you should empty your black water tank depends upon how often it is used, how many people are using it and, to some degree, how it is maintained in between water dumps. These, and a few other issues, are what we’re going to take a closer look at here.

RV water holding tanks guide
There are usually three tanks on an RV: fresh water, grey and black.

What Is An RV Black Water Tank?

An RV black water tank is a holding tank that is attached to the RV’s underbelly. 

The black tank collects all the waste from the RV toilet. The gray tank collects the remainder of the waste water from the showers and sinks in the vehicle.

Black water tanks come in a variety of sizes, ranging from 18 to 64 gallons. They are usually smaller in size than the fresh and gray tanks.

RV manufacturers will at times list the holding capacity of each tank type individually. In other instances the tank capacity is displayed along the lines of 75-60-50 which refers to the fresh water tank, gray water tank and black water tank size respectively.

In other words, given the example above your fresh water tank can hold up to 75 gallons of fresh water, your gray tank can carry up to 60 gallons and you must dump your black tank before it reaches 50 gallons.

A Class A RV, the largest recreational vehicle will have a larger holding tank of capacity than a Class B RV or a camper van.  

How large your tank is will have a significant impact on how often you’ll need to undertake one of the less pleasant tasks an RV enthusiast needs to be prepared for; emptying it. Here’s the average holding capacity of an RV sewer tank depending on RV type.

What Happens When Black Water Tank is Full?

The more obvious problem that occurs when a black water tank is too full is that the liquid it contains will travel back up into the RV toilet, overflow that and then the waste will spread out and go wherever liquid can, which may mean not just your RV bathroom but throughout the vehicle. We don’t think we need to describe how awful that would be.

Another nasty ‘side-effect’ of an overfilled black water tank is that waste water may travel up the vent pipe and exit where that ends, which is usually either the roof of your RV or somewhere on the side. Again, the results will not be nice and may affect any campsite neighbors as well. Not to mention that the cleanup would be an unpleasant process.

In the worst case scenario, if the black RV tank is really full, or if it’s an older tank, there is a chance that it could burst altogether. Black water tanks are usually constructed using plastics and polymers that do weaken with age and over use, another important reason why it’s important to empty yours often!

How To Empty Black Water Tank

How often should I empty my RV tanks?
There’s no hard and fast rule about when to empty your tanks — it all depends on how much you use them.

To avoid the problems we just detailed from spoiling your RV camping adventures, it is crucial you learn to empty your vehicle’s black water holding tank the right way, and, preferably, that you know how before your first trip!

Here are the basic steps you’ll need to follow to empty your black water tank without any nasty mishaps:

What You’ll Need

  • Sewer hose and attachments – these usually come with your RV.
  • Garden hose
  • Gloves (and maybe a disposable mask)

OptionalSewer hose elbow. These are not a must, but can be helpful.

Camco 39736, RhinoFlex Clear RV Sewer Hose Elbow with 4-in-1 Adapter | Features a 360-Degree Fitting Rotation and Built-in Gasket for Odor-Tight Protection | Fits 4 Sizes of Dump Station Inlets

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Emptying and Cleaning Your RV Black Water Tank Step-By-Step


Identify the gray and black water gate valves on your trailer or RV. Although every RV is different, these valves will most likely be near to where your freshwater is connected. The black water tank pipe in most RVs is longer than the gray water tank pipe, but this is not always the case. The valves are usually labeled and feature a handle to open and close them.

You’ll see that the two valves are close to the point where the piping for both tanks joins. The valves are covered by a lid. This is where your sewer hose will be connected. Ensure the gate valves are shut before you remove the lid! Then, turning the tank cover clockwise (off), remove it and set its lid aside.


Since liquid waste flows down, make sure the sewage hose attachment point is higher than the location where the sewer hose will drop its contents.

Connect the sewer hose elbow to the “RV” portion of your sewer hose if you will be using one, then connect the line to the plumbing underneath the gate valves where the tank lid comes off. Connect the other end of the hose to the dump site or septic pit at your campsite.


Allow the black tank to completely empty into the sewer by opening the valve and letting it drain via the hose. When you see the clear elbow attachment or hear the flow halt, you’ll know it’s done. Shut the black tank gate valve as soon as you are sure the tank is empty.


You’ll need to clean the tank at this point, and there are a number of ways to do this according to the particular rig you own. You should always follow the instructions in the manual that came with your RV, to avoid damaging the tank.

For example, some people suggest backwashing the tank itself with a high pressure garden hose. While this is very effective, it may crack a weaker or smaller black water tank. In this case, making use of a tank treatment flushed down through the toilet itself is a better idea. Some RVs are equipped with their own specialist tools too, and a few higher end models have a built-in rinser. Whatever the set-up on your vehicle, proceed here exactly as the manual suggests.


You’re not quite finished yet, as you need to prepare the now empty black water tank for ongoing use. To begin, close all drain pipes to prevent waste from leaking. Fill and flush the toilet three to four times to fill the bottom of the black tank. If you don’t do this, the initial waste that goes down into the tank will harden and adhere to the bottom, causing clogging problems in the future.

Add an eco-friendly enzyme cleanser after there is sufficient.

BioWonder Septic Tank Treatment - Prevent Backups & Reduce Odor - 100% All-Natural Enzymes - Disposal, Drain, RV, Septic, Grease Trap, Toilet, Shower - 2lbs 60 Treatments

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How To Get Rid of Black Water Tank Odor

It may be that your black water tank gets a little smelly, even if it is emptied and cleaned often, especially if you are travelling in hot weather. The enzyme cleaner helps cut down odors a lot, but you may also want to consider making use of a good RV black water tank odor eliminator.

We love the Unique Tank Odor Eliminator Drop in Pods as not only are they very easy to use – you simply drop one into the toilet – they are also designed to work in extreme temperatures, so should be able to tackle tough odors even in the Florida, Arizona or California heat!

Unique Tank Odor Eliminator - Drop-In Pod - Pack of 10 | Hot Weather Formula - Eliminates Odors In Extreme Heat

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How To Maintain Your Holding Tanks

It’s as important to look after your fresh water and gray water tanks as it is to take care of your black water tank, and while emptying and cleaning them regularly is the very best way to keep them in good shape, there are some other things you can do to maintain your RV holding tanks.

For Your Fresh Water Tank

Don’t allow water to sit in a fresh water tank for lengthy periods of time; empty it and dry it after each trip ends.

If the tank or water supply develops an odor,

  • Empty the tank and,
  • Pour a 1/4 cup of bleach into it for every 15 gallons it stores.
  • Drain the tank after filling it with water.
  • Let the tank stand empty for at least a full day before refilling and draining until there is no more bleach odor.

For Your Gray Water Tank

To avoid clogs, be careful not to wash food debris down the drain.

Because this tank contains no fresh water, it may begin to stink, and you’ll need to use a chemical odor absorber.

Chemicals that are too harsh can degrade the valves and seals, so be sure you only choose RV-safe chemicals.

This tank should also be emptied and stored dry.

For Your Black Water Tank

Before using the toilet, make sure there is some water in the tank’s base and that there is an inch or two of tank chemicals.

Only make use of RV-safe toilet paper to avoid nasty clogging problems.

Scott Rapid-Dissolving Toilet Paper, 48 Double Rolls, Sustainable, Septic-Safe, Toilet Paper

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Try to avoid waiting until the last minute to empty the tank. Ideally, you should make a stop to do so when it’s no more than 2/3 full.


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