RVers often ask about the best way to deep clean RV gray water holding tanks. Over time, soap residue, food particles, grease, and other buildup can collect inside a gray water tank, potentially leading to odors, clogs, and other tank problems.
Whether you’re trying to solve an existing issue or simply want to keep your RV gray tank in good condition, deep cleaning your gray water holding tank can help keep your RV’s wastewater system working properly.
Fortunately, deep cleaning an RV gray water tank is a relatively simple process that requires minimal time and supplies. Follow the steps below to learn how to deep clean your RV gray water holding tank and help prevent common gray tank problems.
For instructions and advice about deep cleaning your RV black water tank, please review our guide: How to Deep Clean RV Black Water Holding Tanks.
Key Points About Cleaning RV Gray Water Tanks
- Gray water tanks should be deep cleaned at least twice a year regardless of whether you prefer full hook-ups or dry camping. If you are a full timer, we recommend deep cleaning the gray tank at least once a quarter.
- Deep cleaning gray water tanks is easy, inexpensive, and can be taken care of while you sleep.
- Hookup campers and dry campers need to approach deep cleaning with slightly different methods.
- Common homemade treatments and techniques that are shared online rarely provide you with the best results.
What is Gray Water in an RV?
An RV gray water tank is a holding tank that collects wastewater from sinks and showers inside your RV.
Unlike the black water tank, which holds waste from the toilet, the gray water tank contains wastewater from everyday activities like washing dishes, brushing your teeth, and showering.
Because soap, food particles, grease, and other debris can accumulate over time, regular gray tank maintenance and occasional deep cleaning can help prevent buildup, odors, and drainage problems.
Why is Deep Cleaning RV Gray Water Tanks Important?
While black water holding tanks are a well-known source of unpleasant odors inside of an RV, it is important to consider the smells that can rise from your RV’s kitchen sink and shower drains.
As soap scum, food grease, lotions, or human hair build up, your gray or galley tank(s) can quickly become the source of unwanted odors.
Additionally, as you use your gray water tank, grease and oil can build up and cover tank sensors, causing them to misread. No RVer wants to guess if their gray water tank is full or not, and so keeping sensors free from residue will help them continue to function properly.
Fortunately, because your gray tank does not usually contain solids, deep cleaning your gray tank is very easy — all you have to do is remove the grease that has built up inside of the tank.
This process is like a complete reset for the gray tank and helps restore it to its original condition.
Reminder: Don’t stress if you find yourself needing to deep clean your gray tanks relatively often, grease and build-up can accumulate from regular use even if you are following a strong maintenance routine - and this process is quick, inexpensive, and simple!
How to Prevent RV Gray Tank Odors & Buildup
There are a few things you can do to prevent clogs and odors in your gray tank:
- Install Sink or Drain Strainers: To prevent solid waste from getting into your gray/galley tank(s) and causing odors to rise into your camper, we recommend using sink or drain strainers to catch residual food waste and other debris.
- Scrape Dishes Before Washing: Grease cools and hardens inside of RV pipes and your gray water holding tank, and can cause stinky odors and clogs. Ideally, you should remove grease and food scraps from dishes before washing whenever possible.
- RV Gray Tank Valve Usage: For hookup campers, we recommend leaving your gray tank valve open, which allows the liquid to safely trickle out and prevents grease and residue buildup from causing odors and misreading sensors.
- Add a P-Trap to RV Sewer Hose: Adding a p-trap in your RV sewer discharge hose can help prevent foul odors by creating an additional water barrier to prevent odors from rising into your camper.
- Avoid Cleaning with Harsh Chemicals & Antibacterial Cleaners: There are no chemical drain or antibacterial cleaners that we recommend using in your RV gray water system. These harsh cleaners can dry out or damage rubber gaskets, bushings, and seals, which will not only cause odors to reach your RV, but will also require replacement.
Even when you’re following these best practices, it is important to deep clean your RV gray water tank to fully clean and reset it.
Important Note: Sometimes it makes sense to leave the gray tank valve closed even when you’re camping with full hookups. If you see evidence of sewer flies or other critters at a campground, we recommend leaving the gray tank valve closed to prevent them from reaching the inside of your RV.
Best Way to Deep Clean RV Gray Water Tanks
Deep cleaning RV gray water tanks is very easy, which should make sticking to a regular cleaning schedule relatively painless.
Supplies you need to deep clean your gray water tank:
- Water
- Grease-eating dish soap (Dawn Ultra)
- Time
Through years of experience with customers, we’ve found that the best product out there for removing gray tank grease and residue is Dawn Ultra dish soap. It may seem counterintuitive to add more soap to a gray tank that is already coated in soap scum and grease, but it is an incredible grease-eater that doesn’t leave a layer of residue like other soaps.
You can still use other dish soaps if you don’t have Dawn on hand, but we’ve found most of them ineffective, so stick to Dawn Ultra when possible.
Similar to when cleaning RV black tanks, you can let the cleaning product — the Dawn Ultra in this case — do all of the work while you sleep.
Steps for deep cleaning an RV gray water tank:
1. Close your gray tank valve.
2. Fill your gray tank completely with fresh water and 20 ounces (or more) of Dawn Ultra dish soap.
While the sink is running, begin by pouring 20 or more ounces of Dawn Ultra dish soap down the drain. This will help ensure that the Dawn flows beyond the p-trap under the sink and into the gray tank.
Once the Dawn Ultra dish soap has been added, continue running the sink while monitoring the lower drain that feeds into the gray tank (typically the shower drain). You will know the tank is full, or nearly full, when you see soap suds backing up the drain pipe.
Filling the tank as much as possible is essential because cleaning only occurs where water is touching. If you are attempting to restore your gray tank sensors, be sure that water covers the highest (“full”) sensor in your gray tank.
Important Note: There is no amount of Dawn Ultra that is too much. You may see the soap foaming back out of your sink or shower lines — an indication you’ve poured enough Dawn into the tank —- which is a good sign. This lets you know that the grease-eating dish soap is actively spreading throughout your RV’s pipes and cleaning out all the built-up residue.
3. Allow Dawn Ultra to sit in the gray tank, p-trap, and lines overnight.
4. Open your gray tank valve and empty the tank.
When emptying your tank, it is very common to see grayish-white residue on the bottom of your holding tank discharge pipe. This is the grease that was previously clinging to the inside walls of your holding tank.
5. Rinse your gray tank thoroughly.
The most effective way to rinse your gray tank is to fill it completely with clean water, and then dump the contents. Repeat this 1-2 times to thoroughly rinse your gray tank.
6. Repeat these steps if necessary.
Unlike deep cleaning your black tank where time is magic, there is no benefit to leaving Dawn Ultra in your gray tank for long periods of time.
The magic of Dawn is repeat cleaning, so you may need to repeat this process a few times to achieve the desired results if your tank is especially dirty. Sometimes it can take several deep cleanings before the gray tank is spotless inside.
RV Gray Tank Cleaning Schedule: Hookup Campers vs. Dry Campers
Similar to black water RV tanks, it’s a good idea to deep clean your gray tanks on a regular schedule based on the kind of camping you’re typically doing:
Hookup Campers
If you are primarily a hookup camper (and you follow our advice about gray tank valves), we recommend deep cleaning your gray tank twice a year, once at the beginning of the season and once at the end.
We recommend this schedule as long as you are leaving your gray tank valve open.
By leaving your gray tank valve open, rather than letting water accumulate and allowing grease and residue to build up on your tank walls, water can continuously trickle out without issue. This helps prevent sensor issues and foul odors.
Adding a P-Trap to Your RV Sewer Discharge Hose
When you keep your RV gray holding tank valve open, it allows water to flow directly from your RV into the main sewer drain that is connected to a septic system, but can also allow sewer gases to rise up and waft into your RV.
As long as your sink, shower, and appliance p-traps still have water in them, they should stop the majority of odors from rising into your RV.
However, if one of these fixtures isn’t used for a period of time (perhaps a shower you don’t use in your fifth wheel), and the p-trap is allowed to dry out, you no longer have a water barrier to block foul odors.
Additionally, some RVs are now equipped with factory-installed waterless traps, like HepVo, which use a diaphragm to control the flow of water in one direction. This style of trap does not successfully stop sewer gases as effectively as traditional p-traps.
Creating a p-trap in your RV sewer hose solves both of these problems. Adding a p-trap to your discharge hose works the same way as a traditional p-trap works in your sink by creating a vapor barrier, giving you an additional layer of defense against unpleasant odors that can rise into your RV while your gray holding tank valve is open.
Learn more about adding a p-trap with our guide: How and Why to Add a P-Trap to Your RV Sewer Hose
Dry Campers/Boondockers
If you are a boondocker (dry camper), we recommend you perform a deep clean like this on the last night of every camping trip to avoid grease buildup inside your gray tank.
Many dry campers ask: “Can you dump RV gray water on the ground?” or “Where can you dump RV gray water?”
You must keep your gray valve closed when dry camping because you cannot legally dump black water, gray water, or freshwater holding tanks on the ground.
For more information about proper tank dumping, please refer to our article: Where to Dump Your RV Holding Tanks.
Deep Cleaning RV Black/Gray Water Combo Tanks
Determining the right way to deep clean RV combo tanks can be confusing because you may be uncertain about what to do when using them as both a gray and black water tank.
Here are a few tips about how to clean your combo tank based on your usage:
- Using a combo tank as only a gray water tank: Refer to the steps in the Best Way to Deep Clean RV Gray Water Tanks section above.
- Using a combo tank as only a black water tank: Refer to our guide about How to Deep Clean RV Black Water Holding Tanks.
- Using a combo tank for gray and black water: Start by cleaning it as if it were solely used as a black water tank. If you think there may be excessive amounts of grease or soap scum that were not removed with the black tank cleaning method, then follow the gray water tank cleaning steps as well.
Cleaning combo tanks can be straightforward as long as you make sure to clean them based on your usage. If you’re ever unsure, start by using the black water tank cleaning method and then follow with the gray water tank cleaning method afterwards. Utilizing both deep cleaning procedures is completely fine, and can only help clean your combo tank more thoroughly.
Cleaning Advice from the RVing Community
The RVing community is wonderful about sharing best practices and tips about how to get the most out of your RV experiences. However, in terms of proper maintenance and deep cleaning of RV gray and black water tanks, the advice can sometimes be less than helpful, or even completely inaccurate.
Before taking deep cleaning advice from other RVers, we suggest that you read our article outlining Common RV Holding Tank Myths Debunked. This information will save you wasted time and effort on deep cleaning methods that simply don’t get the job done.
More RV Holding Tank Maintenance Tips
Routine cleaning of both your black and gray/galley tanks will help you stay on top of any waste and grease buildup that can cause your tanks to smell or your sensors to misread.
If you need guidance about deep cleaning your RV black water tank, please refer to our guide: How to Deep Clean RV Black Water Holding Tanks.
If you need help restoring your misreading tank sensors, look no further than our guide: How to Clean and Restore RV Wastewater Sensors.
RV Gray Tank Care & The Unique Method
For proven and tested RV gray tank cleaning guidance, The Unique Method is the only thing you need to solve 99% of your RV wastewater problems.
Created over 30 years of professional wastewater problem solving, The Unique Method ensures that you will have properly functioning holding tanks for years to come. There are no gimmicks involved, all you need to do is follow the clear set of rules and use the right products. It’s that simple!
Maintain a Clean, Problem-Free RV Gray Water Holding Tank
Deep cleaning your RV gray water holding tank doesn’t have to be complicated. With a little time, plenty of water, and Dawn Ultra dish soap, you can break down the buildup that collects inside your tank, pipes, and drains and give your gray water system a fresh start.
Regular deep cleaning is an important part of RV gray tank maintenance, even when you’re already following good habits like using drain strainers, scraping food and grease from dishes, and properly managing your gray tank valve. Hookup campers should deep clean their gray tanks at least twice a year, while full-time RVers and dry campers may benefit from cleaning more frequently.
Most importantly, don’t wait for unpleasant odors, slow drains, or misreading sensors to tell you your gray tank needs attention. With the right maintenance routine and a little regular attention, The Unique Method makes gray tank care one less thing standing between you and a great camping trip.
