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When to Dump Your RV Holding Tanks

  • 5 min read

Article 5 of 9 in Series: Dumping RV Holding Tanks

Read series from the beginning

Key Points:

  • You should be dumping your holding tanks every 3-5 days or when tank levels reach two thirds or three quarters full.
  • Frequent dumping limits waste buildup that could cause clogs, odors, or misreading sensors.

Dumping. Sometimes it’s like a curse word because you so badly don’t want to do it, but you know you have to, and the time comes often much more quickly than you’d like. The time comes so quickly because RV holding tanks are not septic tanks. Septic tanks are huge and do not need to be dumped for months, but we’re talking days with RV holding tank dumps, and there are a few ways to gauge when you need to dump. In this article, we will explain how frequently you should be dumping your RV holding tanks, how to know when you should dump, and some of the reasons why frequent dumping is so important.

How Frequently Should I Dump My Holding Tanks?

The answer to this question is a variable scale because there are many sizes of black and gray tanks out there. RV black tank sizes range anywhere from 4 gallons to 150 gallons, and gray tanks follow the same size pattern. Obviously a 4-gallon tank will need to be emptied much sooner than a 150-gallon tank, so your tank size will have a lot to do with dumping frequency. Some RVers report that a 40-gallon black tank will last two people about 10 days before needing to dump, but again, this all depends on toilet paper usage, water usage, and the number of people using the water systems. Another technique is to always dump when your tanks are two thirds or three quarters full. It’s best to never let the tanks get too close to the full line because an overflow situation in either tank would definitely put the kibosh on an otherwise enjoyable camping trip. The general rule of thumb is you’ll be dumping every 3-5 days, again depending on the size of your tank, the number of people using the toilet and sinks, and how much water is used in the kitchen and the shower. 

If you are an avid boondocker with a smaller-than-desired black or gray tank and you don’t want to be constantly driving back to civilization to dump, you can buy large, aftermarket tanks (if you have room to install something bigger) or you can buy portable sewer totes that can store additional wastewater until you get to a dump site.

Full-timers on sewer hook-up can dump whenever they choose because most tend to stay hooked up to the sewer valve at all times. However, let us take this opportunity to once again remind you that even on full hook-ups, the black water valve should stay closed until you’re ready to dump. If you don’t do this, you could be allowing odors and clogs to start developing. Even if you are always on hook-ups and keep your black water valve closed, it’s still a good idea to let your tanks get at least halfway full before dumping because the more liquid that’s in with the solid waste, the easier it will flow all out when dumped. A tank with just a gallon or two of waste will be much harder to empty completely.

Guide: Why It's Crucial to Keep Your RV Black Water Valve Closed

Why Should I Dump That Much?

Newbies might wonder, if I don’t use too much water or toilet paper, then I won’t need to dump as much, right? Not exactly. Using too little water in your black tank can lead to clogs and odors, so you want to use plenty of water when flushing. And the more waste you accumulate in the tank (regardless of how much water you use), the more likely odors and/or clogs could become an issue.

Dumping often prevents the buildup of waste residue

We recommend always using a high-quality, bacteria and enzyme tank treatment (like Unique RV Digest-It Plus) because it is the best at preventing clogs by liquefying solid waste. However, no matter how well your holding tank treatment works, waste residue will always build up over time, especially if the waste is left to stagnate in your holding tank for several days or is not being regularly flushed out after dumps. The solution to this problem is to dump your tank regularly before waste residue has a chance to excessively collect on the sensors, walls, and floor of your tank.   

Waste build up (even grease and oils in the gray tank) can also lead to sensor issues when it’s left sitting in your tank for too long. If not dumped regularly, waste, toilet paper, and/or grease will start to stick to your sensor probes, causing them to always report tank capacity at a certain level, when in reality, it’s not. Dumping your tanks every 3-5 days or when tanks are two thirds or three quarters full can help reduce the chances of misreading sensors. 

Dumping often helps control odors

When your black holding tank is very full of urine and solid waste, there will be odors in the tank because of the sheer volume of waste. Using enough water to cover the waste will help with odor issues, but at some point, the incredible amount of waste can increase odors regardless of liquid levels, which is why the best practice is to dump every 3-5 days or when your tanks are two thirds or three quarters full. Water is important to the survival and efficiency of the bacteria from RV Digest-It Plus. These bacteria actually take care of smells because they push out the stinky bacteria that are already in there, so you want them to be happy and healthy. If you’re using enough water in your tank to keep these bacteria healthy, you will probably be nearly full in about 3-5 days, depending on the size of your tank and the number of people using the wastewater systems.


Let’s briefly review what we covered in this article:

  • You should be dumping your holding tanks every 3-5 days or when tank levels reach two thirds or three quarters full.
  • Dumping this often reduces the likelihood of waste buildup that could cause clogs, odors, or misreading sensors.

Now that you know all the basics of dumping, we’ll show you how you could save on the cost of that dump station fee by dumping your tanks at home. In the next article we will show you a couple different ways to dump your tanks at home.

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