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What are Grey and Black Water Tanks in an RV?
November 5, 2025192 Min Read128 Insights
Ever wonder how RVs handle waste water? Many RV lovers ask this question before buying their first RV. Well, two key players make it all possible for you:
- a black water tank and a Grey water tank.
- These unsung heroes keep RV residents' lives clean and hassle
- free. Let’s learn about grey and black water tanks
- how they work
- and why maintaining them is essential for every RV owner.
Section 2
What is a Black Water Tank?
A black water tank is the tank in your RV that holds your wastewater from the toilet. The size of this tank depends on the type of RV and your preference; normally, it ranges from 15 to 65 gallons.
The tank is usually located under your RV, exactly below the toilet. It solely collects your toilet wastes. Empty the black water tank when it's approximately two-thirds full to prevent overfilling.
Unlike grey water, black water is dangerous. Therefore, always dispose of it properly at a designated sewer station to protect the environment.
Section 4
What is a Grey Water Tank?
A grey water tank holds all wastewater other than toilet water. It has water from your shower, kitchen sink, dishwasher, and bathroom sink.
The grey water tank is usually under the chassis of your vehicle and stores water from your kitchen and bathroom. The size of this tank depends on the type of your RV, it's normally between 25 and 95 gallons.
Grey water is not as dangerous as black water, but it is also necessary to dump it properly in a dumping station. Some states allow you to dump it on the ground (especially in remote areas), but mostly, it is illegal to dispose of your RV's grey water on the ground.
Section 6
Difference Between Grey and Black Water Tanks
Both grey and black water tanks hold wastewater but have key differences.
| Black Water Tank | Grey Water Tank |
|---|---|
| Black water tanks have waste from toilets (in solid & liquid form) | Grey water is all the waste water other than toilet water |
| The wastes include human waste and toilet paper. | The wastes include soapy water from the shower & kitchen sink, toothpaste, dirt, and debris |
| It is strictly illegal to dump black water on the ground. | In most areas, it’s illegal to dump grey water on the ground. However, a few states allow it, especially in remote areas with no sewer stations. |
| You should empty it when it is two-thirds full. | You should empty it when it is nearly full. |
| Black water is hazardous to human health | Grey water is less dangerous as it mostly contains detergents or mild chemicals. |
| Regular cleaning and specific chemicals are required to make the tank odor-free and clean | You should also rinse it regularly to prevent odors. |
Section 9
Maintenance and Care for Your Grey and Black Water Tank
Clean the wastewater tanks properly to avoid clogs and stinky smells in your RV. Here are some maintenance and care tips for your grey or black water tanks that you should follow:
Grey Water Tank
1. Rinse your greywater tank regularly to prevent clogging.
2. If you sense any grease or soap buildup in your tank, pour warm water and mild dish detergent into the tank before a day of traveling. Then, drive your RV for 24-48 hours and rinse the tank with clean water.
3. You can also use vinegar and baking soda. Chemicals are also available for this purpose.
4. Use tank level sensors to prevent overfilling. Don’t throw large food particles or greasy items into the sink, as they can coat the sensors and cause inaccurate readings.
Black Water Tank
1. Use your RV’s flush system to clean the black water tank after each dump.
2. Buy an RV holding tank cleaning wand for deep cleaning. It works like a garden hose and is inserted through the toilet to spray water in all directions, helping to break down solid waste and tissue buildup.
3. Use enzyme-based chemicals after dumping black water on a sewer station.
4. Don’t let your black water tank overfill, and clean the sensors regularly with a tank-cleaning wand.
Deep Dive
Tools Needed to Dump Black and Grey Water Tanks?
You need various tools to prevent any messy situations while dumping black & grey water. These tools will assist in smooth disposal. The tools are:
1. Sewer Hose
The first thing you should store in your RV is a sewer hose. The sewer hose comes with a swivel fitting, which connects to the tank’s valve and has a storage cap. Normally, the sewer hose is 15 feet in length. It becomes shorter when stored and stretches when wastewater is transferred from the tank to the dump station.
2. Sewer Hose Support
A sewer hose support tool keeps the sewer elevated for smooth drainage. It has different types. In some campgrounds, it is necessary to use a sewer house for proper disposal.
3. Clear Elbow
A clear elbow connects with a sewer hose with one end, and the other end goes into the dump station. The advantage of using a clear elbow is that you'll be able to see when the wastewater stops flowing.
4. Sewer Saddle Bag
A sewer Saddle bag is a device that straddles the sewer hose. When you dump your black & grey water, be ready to face any off-limit scenario. As a precaution, you should have a sewer saddle bag, a device that keeps the sewer hose in place.
5. Gloves
Water-resistant and disposable gloves are a must-have in your toolkit. To avoid any dirtier situation, wear gloves before disposing of grey and black water.
6. Tank Treatment Chemicals
Use enzyme-based chemicals to prevent odor or waste buildup in your black tanks. After draining the wastewater, you can also use a scrub brush to clean your sewer hose.
7. Extra Portable Waste Tank
If you travel frequently or like to camp in remote areas, having a portable waste tank is the best option to avoid undesirable situations. It will come handy if you go to an area where you can’t find any dump station.
Section 38
How to Dispose of the Black and Grey Water Tanks of Your RV?
You should follow certain steps to dispose of your black and grey water tanks properly.
1. First, select a campground dump station for disposing of your wastewater. Never dump the waste on the ground as it is illegal.
2. Wear gloves. Connect one end of your sewer hose to the outlet of the grey water tank and put another end into the hole of the dump station (At least 3 to 5 inches deeper). Place a saddlebag over the sewer hose to keep it secure.
3. Most RV owners advise to drain black water first. However, the right way is to connect the grey water tank with the sewer hose to check smooth drainage. This little checking step can protect you from an absolute no-no situation. First, drain grey water for a few seconds to see if everything is okay.
4. Then, connect your sewer hose with the black water tank, open the valve, and let the waste drain.
5. Once the tank is empty, connect the sewer hose with a grey water tank. If any solid waste gets stuck in the sewer hose, the grey water will remove it.
6. Once the wastewater is dumped, refill both the tanks and again drain.
7. Detach the sewer hose and close both valves. Lift the hose from one end and rinse it properly with a water hose, which is available at many sewer stations.
8. Lift the hose from the hole and store it in your RV. You’re done with emptying your tanks.
9. Wash your hands properly after that.
Section 50
Where to Dispose of Your Black and Grey Water Tanks?
One common question new RV lovers have is where to dump your back and grey water. Several places allow you to dispose of your RV wastewater. These places are the following:
1. Campgrounds & RV Parks
Privately owned campgrounds and RV parks have dump stations for RVers. If you book a campsite with full hookups, you’ll have access to a sewer connection, allowing you to dispose of wastewater as often as you need. However, always check the campground’s specific rules on waste disposal. Some of these campgrounds and parks open seasonally. Use specific mobile apps for up-to-date information regarding their availability and prices.
2. State Parks
Many state and national parks in the US have proper dump stations for RV owners. If your RV is registered, you can freely dump your black & grey water there.
3. RV Cleaning Services
If you don’t like dumping your waste water, you can get RV cleaning services. Many companies in the USA, like The Royal Flush, Hydro Hog, RV Tank Cleaner, etc, offer their cleaning services for motorhomes. These companies specialize in cleaning your tanks properly, preventing odor & clogging, and solving sensor issues.
4. Truck Stops & Rest Areas
Truck stops like Love’s Travel Centers allow you to dump your RV wastewater. You should check their apps for RV-related updates. Moreover, some rest areas & welcome centers also let RVers dispose of their black & grey water. RV service and recycling centers offer RV waste removal.
Some RV rental service centers also let you dispose of the wastewater as an extra service.
Section 60
How to Control Odor in Your Grey and Black Water Tanks?
Your RV stinks like a backed-up sewer if you don’t maintain your waste water system. You can manage odor problems by deep cleaning both tanks.
Control Odor in Grey Water Tank
If you dump food particles, greasy items, and coffee grounds into your sink, your RV will stink badly. To prevent bad smell:
✔Wipe food particles and a greasy pan with a paper towel and throw it in the trash can.
✔ You can also use a grey water freshener in your sink for a bad smell.
Section 66
Control Odor in Black Water Tank
Your black water tank will stink if you don’t use enough water or if waste builds up inside. You can also do the smell test. First, close the door and windows of your RV and then open the toilet’s valve. If there is any bad smell, you need to do deep cleaning.
You can avoid bad smells in your motorhome by following these guidelines:
✔ Flush your toilet for an extra few minutes to prevent any waste buildup.
✔ After dumping black water, use treatment chemicals.
✔ There are two types of tank treatments. Odor suppressors kill the odor by killing bacteria (Enzyme-based suppressors don’t kill bacteria). The second is a digester that uses bacteria to convert solid wastes into a fluid form. Choose the right type based on your tank’s needs.
✔ Keep the toilet bowl clean. If you see any buildup or residues sticking, make sure to clean it properly with toilet-specific chemicals.
✔ You can also pour a small amount of mild detergent with a gallon of hot water into the toilet. Fill the tank more than half and let it sit for 24 hours. Then, drain the water. The tank will be odor-free.
Section 73
How Can You Avoid Clogs in Your Black or Grey Water Tanks?
Maintaining your grey and black tanks is like changing your car’s oil:
- do it regularly
- or you’ll regret it later. Clogs in your RV can occur only if you’re careless in the cleaning process. Follow these guidelines to protect your grey & black tanks from clogging.
Section 75
Avoid Clogs in the Grey Water Tank
Clogging in your grey tank happens when you dump food particles and greasy items in the sink. These particles and grease build up in the tank and can cause clogs.
For better understanding, consider your grey tank like a dish sponge; it will absorb soap, grease, grime, food residues, etc. To avoid clogs:
✔ Wipe down your greasy pans and throw food particles into the trash can before washing dishes.
✔ Use sink strainers to prevent food residues, grease, and hair from getting into the tank.
✔ Empty your grey tank regularly because letting dirty water sit for a long time leads to sludge buildup.
✔ Every once in a while, pour hot water and a small amount of soap into the sink to break up the grease buildup.
Deep Dive
Avoid Clogs in Black Water Tank
Clogs in black water tanks occur when you don’t use enough water, causing solid waste to stick to the surface. You can also face problems by using residential toilet paper instead of RV toilet paper.
✔ Use RV toilet paper as it’s made of short fibers and can dissolve into liquid. However, residential toilet paper can’t dissolve easily and can clog the tank.
✔ Always use holding tank treatments after emptying the black water tank. These tank treatments convert solid wastes into the liquid form and prevent odor.
✔ If you’re at a campsite with a sewer hookup, don’t open your black tank valve all the time. This can lead to clogs due to solid waste buildup.
✔ Before using the toilet, try to pour one or half a gallon of water into it.
✔ Properly clean the toilet using a cleaning wand. This will help to avoid any build-up in the tank.
✔ Never throw paper towels, wipes, or feminine hygiene products into your toilet.
Section 90
How Can You Fix a Clogged Black or Grey Water Tank?
If your black and grey water tank clogs, then it’s going to be an extremely frustrating and dirtier experience. Your whole RV will stink as if you parked it inside a sewage treatment plant. Mostly, you can avoid clogs by yourself instead of getting professional help.
Section 92
Fix a Clog in Grey Water Tank
Grey water tank clogs due to soap scum, food scraps, or hair buildup. To fix this clog:
1. First, close the grey tank valve.
2. Pour hot water and dish soap into the tank and let it sit for 30 minutes.
3. Another remedy for clogging is to pour 1 cup of baking soda and 1 cup of vinegar into the tank. After 1 hour, add hot water.
4. You can also use a drain snake or plunger to break up the buildup in the tank.
5. Once the clog is cleared, dump and properly rinse your grey water tank.
Section 99
Fix a Clog in Black Water Tank
Clogs happen in black water tanks due to insufficient use of water, waste pyramids, and overuse of toilet paper. To fix clogs in your RV:
1. First, close your black water tank valve.
2. Pour hot water and enzyme-based tank treatment into the toilet. Let it sit for several hours. Tank treatment will break the solid waste into liquid.
3. You can also try an ice cube hack by pouring ice cubes into the toilet. And then go for a drive, particularly on rough roads. Knocking ice cubes in the tank will break any clog.
4. If the clog remains, use a tank rinser to spray water into the toilet.
5. If the clog clears, then dump and rinse the tank with water.
If none of these hacks work, the clog may be deep in the pipes, requiring professional help.
Section 107
What are the Signs of a Leaking Grey or Black Water Tank?
A leak in your wastewater tank can be a major headache. It can happen due to cracks in the tank, valve issues, poor installation, chemical damage, etc.
You can detect a leak in your tank by noticing various signs like:
✔ You will smell a musty, sewage-like odor in your RV, especially after using the sink or toilet.
✔ If you notice greasy or soapy water under your motorhome, it is likely a gray water tank leak. If you see a dark water puddle, it is probably a black water tank leak.
✔ If leaks are inside the RV, your kitchen or toilet floor will be damp, discolored, or swollen.
✔ If water drains slowly in your sink or shower area, it indicates a malfunction in the grey water tank. But if flushing the toilet causes bubbling or gurgling, it could be a sign of a blockage or ventilation issue in the black water tank.
If you find a small leak in the tanks, use RV safe sealant to fix it. But if there is a large crack, consider replacing the tank.
Section 114
Portable Waste Tanks
A portable waste tank (or portable waste holding tank) is a sealed, movable container designed to temporarily store black and grey water before transporting it to a dump station.
This tank will be a lifesaver for you if:
⚫ You don’t want to move your entire RV for dumping wastes.
⚫ You often do boondocking where no sewer hookups are available.
⚫ You have a family with kids and don’t want to dump waste water daily.
Portable tanks have wheels and handles, making it easy to transfer the waste water. You can drag them by hand or hook them to the back of your car. Portable waste tanks need the same care and maintenance as black water tanks.
Section 120
Extra Tips for Your Black and Grey Water Tanks
Some additional tips will help you to maintain the wastewater tanks better. Tips are:
⚫ Properly clean your tank sensors, as they notify you when the tank is about to fill. If not cleaned properly, they may become faulty and provide incorrect readings.
⚫ Never use dangerous chemicals like antifreeze, windshield wiper fluid, or bleach in your tanks, as they can damage the rubber seals and cause leaks.
⚫ While living in your RV, adopt a water-saving mindset. Save water as much as possible. Use showers with a shut-off valve and opt for plastic plates to reduce dishwashing.
⚫ Some new RVers open the valves of both tanks at the campsite so they don’t have to worry about disposing of wastes. This act can cause a waste pyramid in your black water tank. Always turn off your valve.
⚫ Always sanitize your black water tank with chemicals after dumping the wastewater.
Section 127
Final Thoughts
Black and grey water tanks are essential for a comfortable lifestyle, providing the convenience of home on the road. Proper disposal of these wastewaters is necessary not just for your RV’s longevity but also for the safety of the environment. Always clean your black or grey water tanks and regularly sanitize them.
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