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Your RV Black Water Tank Survival Guide

Your RV Black Water Tank Survival Guide

As an RVer, you’ll have to learn all kinds of new things. It just comes with the lifestyle. One of these new things is dealing with the RV black water tank. It’s a yucky but essential job. And as you can imagine, it isn’t something you want to mess up! 

Keep reading to learn everything you need to know about your black tank. (And maybe more than you ever wanted to learn!)  

What Is an RV Black Water Tank? 

The RV black water tank is a holding tank for human waste. It holds everything that goes down your RV toilet. Sometimes, an RV doesn’t have a grey water tank. In those situations, all dirty water will be routed to your black water tank.

dumping RV black water tank

How Does a Black Water Tank Work? 

Your black tank holds solid and liquid waste and toilet paper. Your black water tank works a little differently than your grey water tank. With the grey tank, you can sometimes leave the tank open.

You don’t want to do this with a black water tank, though. Instead, you’ll keep the valve closed until the tank is at least 2/3 full. Then you’ll dump the tank.

How Often Do You Need to Dump Black Water?

How often you need to dump black water depends on how much you use your tanks. With more people using the tank, you must empty it more often. If you flush with more water, the tank will also fill up more quickly. But they need a fair amount of water to keep things running correctly – we’ll get into this more later.

toilet flushing

Generally, one person can use the black tank for 10 days to 2 weeks. You could probably make it 10 days with two people, but it might get smelly before that point! We recommend dumping your tank about once a week when you have full hookups. It just keeps things from getting stinky!

You don’t want to dump it too often, simply because it’s an icky job. It’s best to empty your RV black water tank once it’s at least 2/3 full. Most RVs have sensors that will tell you how full the tank is. However, they aren’t always accurate depending on your rig’s age (and your tank’s cleanliness).

Using Your Black Water Tank – Avoid The Poo Pyramid

The way you use your black water tank can impact its function. You may not think an RV toilet can get clogged, but unfortunately, that’s not the case. Dealing with the dreaded “poo pyramid” that can build up is not a pleasant task. Here’s how you can ensure your tank works best. 

First, always keep the tank closed until it’s ready to dump. Keep the tanks closed even when using full hookups at a campground. If you leave the tank open, your sewer hose will have human waste sitting in (and potentially getting stuck in) it. You also risk all the liquids draining and none of the solids. Then the solids can get stuck and solidify in your tank. Yuck! 

Always use RV-safe toilet paper, which disintegrates easier. Regular toilet paper can cause clogs, while RV toilet paper is designed to break down very easily. 

If your RV toilet does clog, don’t panic! Instead, read this article: RV Nightmare: How to Unclog RV Toilet

Firebelly Outfitters RV Toilet Paper, Septic Tank...
  • BEST RV TOILET PAPER - 8 super soft rolls per pack, 500...
  • FAST DISSOLVE TOILET PAPER - Our quick dissolve toilet paper is...
  • RV SEWER TANK SAFE - Our septic tank safe rv marine toilet paper...

Finally, use enough water when flushing. If you don’t have enough liquid in your tank, your poo can get stuck when you dump the tank.

Tank Capacity

RV black water tank size capacity depends on your rig. There’s an enormous range of sizes. You can expect an RV to hold between 15 and 100 gallons. Like we said, a huge range!

If you aren’t sure about your black tank’s capacity, look up the information on the manufacturer’s website. A bigger tank is great for boondocking. The less frequently you need to dump your tanks, the longer you can stay in one place without hookups.

How to Dump Your Black Water Tank

Before you dump your RV’s black tank, connect the RV sewer hose to the wastewater outlet. We recommend using a sewer hose with a transparent elbow, so you can see when it’s done.

hooking up rv sewer hose at dump station
Hooking up your RV sewer hose at the dump station

Once you hook up, you can open the black tank valve. Leave the valve open until the water stops flowing. After your black tank is empty, then empty the grey tank. Starting with the black tank followed by the grey washes out your sewer hose and helps keep things clean while reducing odors.

For a visual on how to empty a typical RV black water tank, check out this video from the RVgeeks: 

RV Holding Tank Dumping 1-2-3

Cleaning Your Black Water Tank

Considering what goes into your RV black water tank, it shouldn’t be a surprise that it needs regular cleaning. Keeping things clean will prevent a smelly RV. It also helps prevent problems in the long run.

To clean your tanks, we recommend using a black tank deodorizer/cleaner to help break down waste so your tanks stay cleaner and less smelly. Regular cleaning can also help prevent clogs.

To give your tank a thorough cleaning, first drain the tank. After that, you’ll add some water and a cleaning agent to the tank. 

There are several types of cleaners on the market, including liquids or tablets that you drop into the toilet. You can buy a commercial RV black tank cleaner online and in most RV stores.

Happy Campers RV Holding Tank Treatment - 64...
  • ODOR FREE: Eliminates odors in the RV holding tank. Absolutely no...
  • Septic tank friendly
  • EFFECTIVE: In extreme hot & cold temperatures ( over 100 Deg)

If you have waste or toilet paper build-up, you may need to do some extra cleaning. There are a variety of tools for rinsing out your tanks with a high-powered water stream. You can use a macerator, a flush valve, or a tank rinser to get the job done.

For extreme cleaning, you can even hire a professional tank cleaner who can pressure wash the inside of the tank, like in the video below:

RV Holding Tank Sensor Fail! Power Washing Black & Gray Tanks & Struvite Removal.

Preventative Maintenance

A few simple steps will help to prevent issues down the road. 

First, clean the tank after each dump. Even though it isn’t fun, staying on top of it makes it more manageable. Another way to prevent issues is to keep your black tank closed. Do this even if you’re staying at a campground.

Next, as mentioned earlier, use an RV toilet paper that dissolves more quickly in water. We also recommend using a holding tank additive and a clear elbow when dumping so you can see the tank and hose are clean. These simple strategies bear repeating because they make a significant difference.

As much as you might hate dealing with the RV black water tank, it’s a necessary evil of RVing. (Unless you decide on an alternate toilet such as a composting or incinerator toilet.) 

rv sewer dumping at dump station

Staying on top of cleaning and dumping your tanks is critical to a happy RV life. If you aren’t already using these tips, it’s time to start now!

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Gerald Brockman

Friday 19th of February 2021

Good information. Just bought a 21' trailer and wondered how to check. It is still winterized so can I see climbing underneath and looking? Might wait till dewinterizing before 1st trip. Then, knowing black tank is empty, I could leave gray open and pour water into sink and shower and hope both go out. Thanks Mark for that story because I that possible scenario wouldn't have been on my radar.

Mortons on the Move

Sunday 21st of February 2021

Depending on the trailer design you may or may not be able to see the pipes. Doing the water test you suggested would probably be the best way to test that. Hopefully, they didn't build it like that as it is technically not correct or RVIA certifiable.

Mark Lawler

Wednesday 17th of February 2021

The hard lesson my stepdaughter learned in her new rig was that there was more than the toilet connected to the black tank. Instead of the bathroom sink draining to the grey tank, it drained straight down into the black tank under the rear bathroom. Couple that with suspecting a fouled tank level sensor, a state park with no dump station, and this being their first RV trip in that rig... Add in that a bathroom sink sits higher than the toilet... Let's just say they had a full tank and full toilet bowl in record time and couldn't use their own toilet or sink for the last two days of the trip... Lessons learned: figure out if all your sinks drain to the grey tank or if the manufacturer cheated and took the easy path to the black tank with one of them; sometimes tank semsors are telling you the truth; you really do want to turn the water on for a short burst vs letting it run any length of time; facial masks and washing them off may be an activity left at home or a community sink...

Mortons on the Move

Friday 19th of February 2021

Wow...that sounds like quite an ordeal for your daughter. Understanding your RV's tank configuration and recognizing that sensors aren't always accurate are important things to know before heading out on your first RV trip.

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