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Deep Cleaning RV Wastewater Holding Tanks

July 14, 2020

Deep Cleaning RV Holding Tanks - Unique Camping + Marine Guide

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Key Points:

  • Black tanks should be deep cleaned at least twice a year to ensure continued functionality and odor-free RVs
  • Gray tanks may need deep cleaning more often than twice a year depending on the type of camping you’re doing
  • Deep cleaning black and gray tanks is easy and can happen while you sleep

We get a lot of questions about the best way to clean RV holding tanks. Keeping your holding tanks clean and free from build-up is key to avoiding the clogs and foul odors that can sneak into your RV. Without regular deep cleaning, waste can find ways to hide in the crevices and low points of your tank and potentially cause problems later when you’re thinking about anything but cleaning out your RV holding tanks. Whether you currently have a problem or just want to practice  good tank care habits, deep cleaning your tanks is a great place to start.

You might be sure you have a clog either in your tank or in your toilet. Or you might be clueless about what kind of problems you have going on inside your RV’s holding tanks. In either case, we recommend also thumbing through the following guides that will help you diagnose the specific problem, how to fix that problem, and what you need to do going forward to avoid those same issues in the future:

Using Bleach to Clean Holding Tanks

People often ask if they should use bleach to clean out their wastewater holding tanks. That’s a triple no. We strongly encourage you to stay away from using bleach and other chemical cleaners in your wastewater tanks because ironically, they actually make things worse when it comes to preventing odors and breaking down waste (The Unique Method explains more about why it’s best to avoid chemical cleaners in your wastewater tanks). However, bleach does a great job sanitizing your freshwater tank to ensure that your tap water is clean and free from bacteria.

Guide Continued Below

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Deep cleaning your black and gray holding tanks regularly is one of the ways to prevent future problems from arising at just the worst time. We’ll show you how easy it is to perform a deep cleaning with much less effort than you might suppose.

Deep Cleaning an RV Black Water Tank

Deep cleaning your RV black tank may sound pretty involved, but it’s actually quite simple.


We recommend using Unique Tank Cleaner because it’s the strongest bacteria-based cleaner on the market and will help you achieve the deepest clean. The steps below will walk you through the process of deep cleaning your RV black tank using Unique Tank Cleaner.

  2. Fill your black tank with water.
    This might sound obvious, but you can only clean what the water is touching, so the more water you add, the more your tank will be cleaned. 

  1. Dump 1 entire bottle of Unique Tank Cleaner into your 40 gallon black tank by pouring it through your toilet and let it sit in the tank for 12-72 hours.
    While Tank Cleaner typically works in about 12 hours, the longer you let it work the better! No amount of time is too long because letting it sit for days, weeks, or even months won't cause any damage to your RV.

    Note: No amount of Unique Tank Cleaner is too much, so feel free to use a whole bottle on a smaller tank or more on a larger tank. If you have questions, we are always willing to help you find the best solution for your RV.

  1. Open your black tank valve, dump the tank, and rinse.

    • If your RV comes with a built-in tank rinser (or flusher), it’s best to run it for about 30 minutes or until the tank is thoroughly rinsed out.
    • If you don't have a built-in rinser, we recommend using a RV holding tank cleaning wand or external tank rinser that connects to your discharge line.
    Always keep your black tank valve closed unless you’re dumping!

It’s that simple! We recommend performing a deep clean on your black tank twice per year: once at the beginning of the RVing season and once at the end. Our already-assembled Biannual Tank Maintenance Pack includes everything you’ll need (except a rinsing wand) to deep clean your tank twice a year. If your RV is stationary and rarely moves, it's a good idea to perform a deep clean like this every 60 days since waste tends to accumulate because it never or rarely sloshes around. If this doesn’t solve the problem or you’d like more details, please see our guide to Cleaning and Restoring Black Tank Sensors.

Deep Cleaning an RV Gray Water Tank

If you think your black tank will likely be the only culprit when it comes to unpleasant smells inside your RV, consider the odors that could rise from the kitchen sink drain. Yes, your gray tank can easily start to stink as a result of the build-up of soap scum, food grease, lotions, or even human hair from the shower. This can cause more than just unpleasant odors; it can also lead to misreading sensors. Thankfully, because there aren’t a lot of solids inside your gray tank (at least, there shouldn’t be), restoring your gray tank to its full glory is very easy to do; just remove the grease that has built up inside the tank!

Note: To prevent solid food waste from getting into your gray tank, use a sink strainer to catch residual food waste and wipe grease and debris off your dishes before washing whenever possible.


  • Water
  • Grease-eating dish soap
  • Time

From our experience with customers, the best product out there for removing gray tank grease residue is Dawn Ultra dish soap. Yeah, we know; it doesn’t seem to make sense to add more soap to a gray tank that is already coated in soap scum, but it’s an awesome, completely safe grease eater and doesn’t leave a residue layer like other soaps. And just like deep cleaning the black tank(s), you can let the cleaning product (Dawn Ultra dish soap) do the heavy-lifting overnight while you sleep. The steps below will walk you through the process of deep cleaning your RV gray tank using Dawn Ultra dish soap.

  1. Close your gray tank valve. 
  2. Fill your gray tank all the way to the top with fresh water.
    The ultimate goal here is for water to cover all the areas you want cleaned. If your tank isn’t totally full, only the parts of the tank at or below the waterline will be cleaned. If you’re looking to restore your gray tank sensors, be sure that water covers the highest sensor in your gray tank.

  1. Pour at least 20 ounces (or more) of Dawn Ultra dish soap down your RV’s kitchen sink.
    There is no amount of Dawn Ultra that is too much. It’s possible that you’ll see it foaming back out of your sink or shower lines (an indication you’ve poured enough Dawn Ultra into the tank), which is a good sign because it means that the grease-eating dish soap is spreading throughout your RV’s pipes and cleaning out all the built-up residue. 

  1. Let Blue Dawn sit in the tank and lines overnight. 
  2. Open your gray tank valve in the morning and empty your gray tank.
    It’s very likely that you’ll see a grayish-white residue on the bottom of your holding tank discharge pipe. This is literally the grease that was previously clinging to the inside walls of your holding tank.

  1. Rinse your tank very well by filling it completely and dumping it several times.
  2. Repeat these steps if necessary.
    Sometimes it can take several cleanings before the gray tank is completely spotless inside.

Like black tanks, it’s a good idea to deep clean your gray tanks on a regular schedule, depending on what kind of camping you are typically doing. 

  • If you are primarily a full-hookup camper, deep clean your gray tank biannually (once at the beginning of the season and once at the end).
  • 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.

Routine cleaning will help you stay on top of any grease buildup that can cause your tank to smell or your sensors to misread. If your sensors are currently misreading and you’re in need of specific guidance for restoring your gray tank sensors, start with deep cleaning your gray tank as described in the above steps. If this doesn’t solve the problem or you’d like more details, please see our guide to Cleaning and Restoring Gray Tank Sensors.

Modified Deep Cleaning for Full Time RVers

If you are a full-time RVer, deep cleaning tanks can be a lot trickier when you’re trying to use them at the same time. We recommend that full-time campers clean their black tank(s) regularly with Unique Tank Cleaner and their gray tank(s) with Dawn Ultra dish soap (every 5-10 dumps). This will help maintain properly working holding tanks and keep odors at bay.

We understand that while cleaning your black tank(s), you’ll still need to use them, so you may not be able to completely fill them with water and walk away for 2-3 days. Instead, full-time RVers should fill black tank(s) half full with water, add one bottle of Tank Cleaner per black tank, and continue regularly using your toilet, ideally letting the solution work for a full 72 hours before dumping. The best option is always to deep clean without using the tanks, but even deep cleaning while using them will still help prevent buildup and other tank issues. Just remember, Tank Cleaner can only clean areas it can reach; areas of the tank walls that are not touched by water will not be cleaned. 

Deep cleaning gray tanks is a little easier when it comes to full-time RVing. Refer to the Deep Cleaning an RV Gray Water Tank section above because it’s the same process for full-time RVers!

The Unique Method will help prevent the majority of tank problems before they happen, so we recommend following this method, which recommends regular deep cleaning. For more thorough details on full-time RVing care habits, refer to Full Time RVing: The Definitive Guide To Treating Your Tank

Deep cleaning both your black and gray tanks will not only help you enjoy your RVing adventure all the more without having to deal with nasty odors or the probability of RV clogs, but it will also help your wastewater systems run optimally for years to come!

Adopt The Unique Method

You bought your RV so you could enjoy life and spend time with family and friends. The last thing you want to do is waste precious time and money on fixing wastewater holding tank problems. Keeping your tanks in peak operating condition doesn’t have to be hard, confusing, or expensive if you follow our proven process: The Unique Method.

The Unique Method is a comprehensive tank care plan that we developed after years of conversations with real customers facing real problems. The Unique Method provides you with simple, preventative steps to stop odors, clogs, and sensor problems before they start so you can spend less time worrying about your holding tanks and more time enjoying the freedom and adventure of RVing. Try it yourself and see why thousands of campers trust their RVs with The Unique Method every day.

If you need more help with anything covered in this guide or simply have a comment, we’re here to help you anytime!

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