Unclogging an RV Black Tank: Step-by-Step Guide

Having a clean, fresh toilet available when you travel is a luxurious benefit, but like all toilets, an RV black tank can clog up pretty quickly if not maintained well. Nobody needs that when you’re parked in the woods!

To unclog an RV black water tank:

  • Connect your sewer hose to the RV and dump station sewer connections.
  • Prop up the end at the sewer side and open the grey water valve to fill the hose with water.
  • Close the grey water valve
  • Pick up the water filled sewer hose and open the black water valve.
  • Slosh the sewer hose around to force the water back up into the black tank.
  • Quickly drop the hose and allow the water to create a suction and pull the clog from the black tank.

Most clogs occur because a large mass of solid matter is clogging the outlet pipe of the black tank. In this guide, I some of the most popular methods to unclog an RV black tank and keep it clean, as well as tips on avoiding a clogged toilet.

4 Methods to Unclog an RV Black Tank

There are various methods available to unclog an RV black tank. Some help you get by until the nearest workstation is available, and some flush the system out so the cycle can start anew. 

Here are a few methods that RVers have found useful for unclogging an RV black tank:

Pour Boiling Water Down The Toilet

This is a technique that’s been used by RVers for decades because it is simple, easy, and anyone can do it. Also, it does not require any technical knowledge.

  • Turn off the fresh water supply to the toilet, if possible.
  • Hold down the flush handle or pedal to open the valve to the black water tank.
  • Pour a few pots of boiling water into the black tank.
  • The hot water should accelerate the breakdown of the solids clogging your RV black tank.

I recommend doing this at night so the waste has time to soak undisturbed in the hot water. Keep in mind that if your tank is full, the water won’t heat up as much as if it were ½ to ¾ full.

Adding Clog Digesters To The Black Water Tank

Adding a liquid holding tank treatment like Unique RV Digest It will eat away at the poop, paper and other solids inside your black water tank and free up any clogs quickly. Because it is a blend of microbes and enzymes it won’t damage the materials of your RV sewage system like some harsh chemicals can.

  • Hold open your toilet flapper with the flush handle or foot pedal.
  • Add the recommended amount of RV Digest It.
  • Wait a few hours for the clog to be consumed and liquified.
  • Connect your Sewer hose to your rig and a dump station.
  • Open the black water valve and the clog should be cleared.

This type of treatment will also help keep the sensors and seals in your tanks clean and prevent leaks and electrical faults due to sewage buildup. It also does a great job of eliminating odors from wafting out of your holding tanks without the use of perfumes or obnoxious scents.

Whatever brand you choose to use, just make sure they are septic-safe, or they could ruin the wastewater system of your RV.

Unique RV Digest-It Black Water Tank Treatment - Concentrated Liquid RV Toilet Treatment -...
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  • Stops black water tank sensor probes from misreading by liquefying waste before it clings to probes. Works in RV gray tanks by digesting...

Use Ice Cubes To Agitate The Black Tank Solids

The ice cube method works by brute force and agitation. Rumbling down the road with chunks of ice in your black tank will slosh and pound the solids around in your tank and clear out the clog at the same time.

  • Pick up a bag of ice cubes from the local convenience store.
  • Dump them down the toilet into the black tank. 
  • Start up your rig and drive down a bumpy and windy road for an hour before the ice melts.
  • Head to the nearest dump station and empty your tanks before the solids get a chance to settle to the bottom of the tank again.

I like to do this at the start and near the end of the season when my black tank is around half full. It’s a simple and cheap way to shake things up down below.

Flushing A Black Tank With Pressurized Water

Using a wand that can enter and spray water all around your black water tank should flush out any clogs and loosen any built up solids from your tank. 

The Camco swivel stick is one of the most popular products for this use because it has a rotating spraying head and an on/off valve on the handle.

  • Connect your sewer hose to the RV and dump station.
  • Open your black water valve.
  • Connect your swivel stick to a water supply using a hose.
  • Hold open the toilet flapper and insert the wand down into the black tank.
  • Turn on the valve and move the wand up and down inside the tank to rinse away any clogs and buildup.
  • Turn off the water valve and remove the swivel stick from the tank and toilet.

The swivel stick comes in a rigid and a flexible option to suit the setup of your toilet and tank system. 

If you have a tool like the swivel stick it’s a good preventative maintenance step to use it after every couple visits to the sani dump. Give your tank and sewer pipe a rinse after you dump but while you’re still connected to the drain pipe.

Camco Camper/RV Holding Tank Swivel Stik Rinser | Features Powerful Rotary Cleaning Action &...
  • POWERFUL ROTARY CLEANING ACTION: Enjoy superior cleaning power with this RV tank cleaner. Its powerful rotary cleaning action shifts even...
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  • SIMPLE TO USE: No need to worry about complicated setups— it easily attaches to most garden hoses with a standard ¾" female connection....

How to Avoid a Clogged RV Black Tank

Dumping out a black water tank is already disgusting, and having a clogged toilet on top of it is going to sour your trip really quickly. To avoid an obstruction in an RV black tank, here are a few tips to keep in mind.

Upgrade To A Macerator Toilet

RV macerator toilets have a built in motor pump and set of blades that grinds up the waste in your toilet before sending it to the black tank.

Reducing the solids in the black tank, especially toilet paper wads, will prevent clogs from happening in the first place. See my introduction to RV macerator toilets for more in-depth details.

Keep Uncloggers Ready

Simple methods like flushing with a swivel stick do work great and can often clear obstructions and prevent them from occurring in the first place. 

The regular use of a black tank treatment like RV Digest It will keep your system free of clogs and prevent buildup on the sensors in your black water tank. Your pipes, valves, tanks and monitoring system will operate smoothly and more efficiently.

Extend the Flush Cycle

In a recent article titled How Much Water Does An RV Toilet Use? I went into depth on finding the common ground between water conservation and a proper RV toilet flush.

Having access to a stock of freshwater (potable or non-potable) ready to fill up the bowl and flush down to the holding tank can get you out of a jam.

Prevention is always easier than repairing, so pour in boiling water on occasion to break down potential clogs or try the ice cube method before your next dump visit.

Cut Down on Toilet Paper

Toilet paper is the primary cause of clogs in the drain and tank, so cutting down on the usage of TP and increasing the use of water is essentially the best way to ensure the black water tank doesn’t clog. You could also invest in a portable bidet so the use of toilet paper is minimal to none.

Some RVer’s also prefer to put their toilet paper in the garbage versus down the toilet. This practice is common in many countries that have less developed sewer and septic systems. Using a closed garbage bin and emptying frequently is an easy way reduce odors.

Buy Septic-Safe Toilet Paper

Septic safe toilet paper is found in most grocery stores and is made to breakdown better in a septic system. It won’t be as soft or as strong as the 3-ply bear brand stuff but it will be less likely to block your tank up.

There are also RV specific toilet papers. These tend to be more expensive than ones advertised as safe for septic systems since you usually have to buy them at specialty places like Camping World. Septic safe TP works the same or maybe even better than RV specific TP.

How Often Does an RV Black Tank Need to Be Emptied?

A general rule of thumb is to dispose of the waste when the black water tank is ⅔ of the way full. A quick way of telling when it’s time to clear the tank is if you notice the water level rise in the toilet bowl or stay stranded after flushing.

Most black water tanks in modern RVs are equipped with sensors, so unless it malfunctions, there’s no need to look out for the water level as the sensor will let you know when it’s time to dump out the black water tank.

It generally depends on how often it is used. For example, an RV black tank used by one person can be emptied out after a week or more, and if it’s used by a family, it may need to be dumped every few days.

How to Keep an RV Black Water Tank Clean

Although a black water tank is essentially responsible for holding waste, you still need to keep it clean so that it doesn’t clog or waft unpleasant odors throughout the RV.

Some ways you can keep an RV black water tank clean include:

  • Hold down the flush lever or button for a minute everytime you empty the black tank to rinse away any residual buildup in the tank.
  • Dump a bag of ice down your toilet and drive around before you visit the dump station.
  • Use a sani-safe tank treatment like RV Digest It regularly to help break down the solids in your tank before dumping.

How to Dump Out an RV Black Water Tank

Emptying out an RV black water tank is easy, but there is a specific method you’ll need to follow. You’ll want to wear gloves and keep the sewer hose away from your face to avoid inhaling sewer gasses.

  • Connect your sewer pipe to the RV holding tank connection.
  • Connect the other end of the pipe to a sewer drain.
  • Open the black water valve to allow the tank to empty.
  • Flush your toilet continuously for one minute.
  • Close the black water valve.
  • Open your gray water valve and allow the tank to empty.
  • Close the gray water valve.
  • Disconnect the sewer pipe from the RV and flush it out with a hose.
  • Disconnect your sewer pipe from the dump station and stow it away.

Gray Water Tank vs. Black Water Tank: What’s the Difference?

Before using heavy chemicals and motor-powered devices to unclog the toilet, it is important to know the difference between a black water tank and a gray water tank so the system is less likely to malfunction.

A gray water tank is essentially a wastewater holding tank for the sink and shower. It collects dirt, food grime, and soap residue that make the water muddy and gray. There is no fecal matter or raw sewage that enters an RV gray water system or tank.

A black water tank is a separate holding tank of the RV, and it holds solid and liquid waste flushed down from the toilet. On occasion a bathroom sink will be connected into the black water system for convenience and to add more liquid to keep the system operating efficiently.

Frequently Asked Questions

What happens when an RV black water tank is full?

When an RV black water tank is full your toilet will no longer flush and will likely back up creating a big mess on your floor. If you are using a pressurized system like a masticating toilet it’s possible that the black water will be forced up your vent pipe or cause damage to the tank and valves.

How long will a 40-gallon black water tank last?

It depends on how many people are using it. For a single person, a 40-gallon water tank can last about 18 days (about 12 for two people and approximately 9 for four people).

How long can an RV black tank stay full?

Generally, it is recommended to dump out the waste as soon as possible and not keep it full for more than a week. If this isn’t possible, you can safely maintain a full RV black tank for eight to 10 days but be sure to add some RV Digest It to prevent solids from building up in the tank.

Does pouring boiling water down an RV toilet unclog it?

Yes, pouring boiling water down an RV toilet is one of the easiest and quickest methods of unclogging the black tank. It gives you enough time to reach a safe place and then use extra tools to properly remove the clog. Also, it does not leave a chemical odor.

Can you put vinegar in an RV Black Tank?

Yes, vinegar can be poured down an RV black tank as a cleaning agent. Couple that with a tablespoon of baking soda and it’ll remove any buildup in the tank. Just make sure not to use bleach to sanitize the tank unless the vinegar has been flushed because the resulting gasses can be toxic.

Final Thoughts

A clogged RV black tank can easily become your worst nightmare, but knowing how to unclog an RV black tank and prevent it from becoming obstructed on your future trips can vastly improve the experience of traveling with your camper.


Beau is an electrical engineer with a knack for DIY repair and construction. When he's not tinkering with his projects he's on the road travelling and enjoying an exciting lifestyle with his young family.

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