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The RV Black Tank Flush System – All You Need to Know

The RV Black Tank Flush System – All You Need to Know

Every RVer knows that of all the duties an RV owner has to tend to, dumping the black tank is the least enjoyable. That said, there are ways to make tasks related to the black tank considerably easier to endure. A prime example is the RV black tank flush.

Not every RV has a black tank flush system, but those that do provide a beneficial service to their owners from a couple of perspectives. But we’ve actually met RVers who didn’t realize that their RV had a black tank flush and others who weren’t really sure how to use it or whether it was all that useful.

So, in today’s post, we’re talking about RV black tank flushing systems – what they are, what they accomplish, and how to use them!

What is an RV Black Water Tank Flushing System?

An RV black tank flush is a cleaning system that works in tandem with your regular RV tank dumping procedure. For example, you generally dump your black tank and then flush out the sewer hose by dumping the contents of your gray tank immediately thereafter. (You do dump the black tank first and the gray tank second, right? If that’s not what you’ve been doing, start doing that the very next time you dump!)

This removes the contents from the black tank and then, as the gray tank empties through the system, it flushes things out the sewer hose relatively well. The operative word there, though, is “relatively.” And what about the inside of the black tank itself?

This is where the RV black tank flush comes into play. Essentially, it clears out what’s left behind from the initial dump-and-flush by providing a secondary flush that cleans the hose out more thoroughly, as well as the inside of the black tank, too.

If you’re not sure whether your RV has a black tank flush system, have a look around. Usually (but not always), a black tank flush system is located in the water bay, somewhere in the general vicinity of the black tank dump valve.

Our RV black tank flush system connection.

Our RV’s black tank flush connection, marked “sewage tank rinse,” is located in the water bay of our rig.

How Does an RV Holding Tank Flush Work?

The black tank flush system requires a separate garden hose that connects to the flush inlet valve. We highly recommend using a dedicated hose for this purpose, perhaps of a unique color, but certainly not your drinking water hose!

Sale
Camco 22990 25ft RhinoFLEX 5/8" ID Gray/Black Water Tank Clean Out Hose | Ideal For Flushing Black Water, Grey Water or Tote Tanks , Orange
  • Ideal for flushing black water, grey water or tote tanks
  • Keep contaminants separate from your drinking water hose or garden hose

A nozzle (or several) inside the tank supplies a spray of water that rinses down the tank walls and helps to flush out more waste that might otherwise have been left behind.

Most RV black tank systems also have an anti-siphon valve that serves as a back-flow preventer. These are often installed inside the RV in a cabinet located above where the tank flush inlet is installed.

The purpose of the anti-siphon valve is to ensure that waste water in the tank can’t be siphoned back into the freshwater system. We always use an additional anti-siphon valve like the one below in line with the supply hose as a fail-safe secondary backup to protect the freshwater system we’ve connected our flush hose to. We simply screw it onto our RV black tank flush connection and then connect our hose to it.

Valterra Products, Inc. A01-0141VP Plastic Carded Removable Anti-Siphon Valve
  • Package Dimensions: 4.5 L x 1.5 H x 3.75 W (inches)
  • Package Weight: 0.1 pounds

Note that if the anti-siphon valve in your RV fails, it can allow odor from the black tank into the RV, so if you’ve got a mysterious odor in your RV, that’s one of several possible sources you’ll want to check. This would be a replacement for that valve:

RecPro RV Vacuum Breaker Check Valve | Protect Fresh Water From Pollutants 571-VAC-CHK-A | Made in America
  • Although this piece is small and simple-looking there are several points that need to be addressed when it comes to proper water safety and...
  • Second, this vacuum breaker is a high-hazard protectant. Because of this, it can be used in a low-hazard application as well.

An RV black tank flush system comes with an anti-siphon valve/vacuum breaker like the one above that is installed inline with the incoming water supply. It’s typically installed inside the RV in a cabinet located somewhere right above where you connect an external hose to the black tank flush connection. (Ours is inside our bathroom cabinet, right under the sink, and it’s mounted up high – so the plumbing for it goes up high under the cabinet with the anti-siphon valve/vacuum breaker installed at the top of the water lines.)

Again, its purpose is to ensure that water in the black tank can’t get siphoned back out through the fresh water connection when flushing your black tank. The inline anti-siphon valve/vacuum breaker lets air into the line, breaking the suction, which prevents siphoning.

How Long Should I Flush My RV Black Tank?

We suggest flushing for as long as it takes for the water to run clear. How do you know when it’s running clear if you can’t see through the sewer hose? We use, and highly recommend, a clear elbow for this exact reason. It may not be pretty to look at, but knowing what’s happening inside your sewer hose as you’re dumping the black water is key to properly flushing the black tank.

As you begin dumping your black tank, you’ll begin rinsing with your black tank flush system. Close the black tank valve and allow the tank to fill a little, then open the valve again and watch your clear elbow. If the water isn’t running clear yet, repeat the process — close the black tank valve, partially fill the tank, then pull the black valve again. Once clear water is running through the elbow, your black tank is well rinsed and you’re done! Now you can turn off the black tank flush, close the black valve, and dump the gray tank.

We then disconnect the sewer hose, and rinse everything off (including the inside of the sewer hose) with our dedicated tank flushing hose, and we’re done.

How Often Should I Flush My Tank?

To facilitate good flushing action, it’s typically recommended to wait until the black tank is at least 1/2 to 3/4 full before dumping it. This varies, of course, depending on how many people are traveling on your RV, and how large your black tank is. Dumping frequency can also be reduced by taking advantage of other facilities when available, such as campground bathrooms.

That said, we (the two of us) can go a comfortable 2 weeks on our 45-gallon black tank, with room to spare. That’s when we’re boondocking with no other facilities available except our own bathroom.

Rather than utilize a dump station, we always try to dump the black tank when we’re at a full hook-up (electric, water & sewer) campsite. That’s because dumping and flushing properly can take a little extra time, and you’ll want to be cognizant of others who may be waiting to dump their tanks.

Another reason we try to avoid dumping (especially the black tank) at a dump station (vs a full hook-up site) is that you can’t always be certain that they’ll have a threaded spigot available to attach your flush system hose to.

Lastly, dump stations don’t generally provide the opportunity to hard-connect your sewer hose to the sewer opening the way you can at a campsite (which we do using this adapter). That means you’re a lot more likely to catch a nose-full when you pull that black valve for the initial dump. We also use a sewer hose support at full hook-up campsites, which isn’t practical at a dump station.

What Can I Do If My RV Doesn’t Have a Tank Flush Built In?

If your RV doesn’t have a black tank flush system, you can use an RV tank rinsing wand like this one to rinse your tank in a similar way, which you stick down into the tank through the toilet.

Sale
Camco RV Flexible Swivel Stik with Shutoff Valve - Creates Powerful Cleaning Action that Dislodges and Flushes Stubborn Waste Deposits and Combats Odors (40074), 55-1/2 Inch
  • Powerful rotary cleaning action dislodges and flushes the stubborn waste deposits and odor-causing particles left after holding tank is emptied
  • Solid section including handle measures 24" long; the flexible section measures 34" long with a 2" diameter nozzle

These have a standard ¾” female garden hose connection to connect to your dedicated tank flushing hose, and have rotary spraying ability to flush the remaining waste from the sides of the black tank. The solid section of this wand is 24” long, and the flexible section is another 34” that allows the nozzle to reach holding tanks that are offset from the toilet.

Can I Install an RV Holding Tank Flush Myself?

In addition to wands like the one shown above, there are various aftermarket tank flush systems available. Most require drilling a hole into your black tank. You can choose to install it yourself or ask an RV dealer or technician to do it for you.

This is a very inexpensive and simple rinse system, but the installation still requires drilling into your black tank. We’ve never used this product ourselves so we can’t vouch for it – but this is one example of an inexpensive aftermarket black tank flush system.

Sale
Camco 40126 Tornado Rotary Tank Rinser with Hose
  • The easiest, most sanitary way to clean the RV holding tank
  • Dislodge and flush stubborn waste deposits and odor-causing particles left after holding tank is emptied

Another option for an aftermarket black tank flush system is this one from Valterra. Again, we’ve never used this system ourselves – be sure to read reviews and also remember that installation of this product involves drilling into your black tank:

Sale
Valterra A70 No-Fuss Flush with Check Valve , Yellow
  • Product Type :Valve
  • Package Dimensions :11.4 Cm L X15.2 Cm W X25.1 Cm H

Remember also that a rinsing wand such as the one shown in the previous section is popular for a reason. If you don’t want to drill a hole in your RV black tank, look into the rinsing wands as a simple option, with no installation required.

Why Should I Flush My RV Black Tank After Dumping?

Keeping your black water waste holding tank well rinsed not only helps to reduce odors, but also helps to keep the dump valve in good working order. It also prevents solid matter from hardening down onto the bottom of the tank, making the entire dumping system work more effectively.

Also, as “stuff” starts to build up on the walls of your tanks, the ability of your holding tank sensors to provide information can be significantly reduced. Keeping your tank sensors clean is very important if you want to be able to keep an eye on how full your tanks are. And flushing your tanks well – particularly your black tank – is one way to keep your holding tank sensors clean.

So, whether you have a built-in RV black tank flush system (some RVs even have gray tank flush systems!), use a wand, or pour a few extra gallons of water down the toilet to flush the tank until the water runs clear, flushing your RV’s black tank is a good idea for lots of reasons.

And speaking of dumping, be sure you know the rules when it comes to releasing gray water on the ground!

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PinkyPoch

Monday 22nd of August 2022

Hi Geeks, We recently purchased a 2014 Keystone Maple Country. We have a flush at the back of our RV, but when we hooked up water nothing came out and we assume no water went in as none came out any other places either. They were wondering if the anti siphon valve would be the first place to check and where else should we be looking or what else can we do to help this situation.

TheRVgeeks

Monday 22nd of August 2022

Hi Pinky. If, when you turned the water on to the hose connected to the tank flush, you didn't hear any water flowing... it's possible that you may have a blockage. Either a part of the flush system plumbing is blocked (i.e. there may be a back-flow preventer built in to ensure black tank contents can't find a path back into the fresh water system) or the sprayer valve itself is clogged/blocked. If the sprayer head is clogged/blocked, you may need to soak your black tank with a heavy dose of tank treatment (like Happy Campers) to try and unblock it.

Karen Campbell

Friday 12th of August 2022

Last night I flushed my tank but the black tank was closed. There was a big pop and water started to pour out under my trailer. What have I done and is it going to be expensive!!!!!!

TheRVgeeks

Friday 12th of August 2022

Oh no, Karen! Sorry to hear that. It's hard to tell what the "pop" could have been, but likely some plumbing connected to the black tank may have gotten over-pressured and came loose. Might not be expensive as far as parts, etc... but the labor to get at it could be, depending on where on your RV the tank is located.

Question... was the water that started to pour out clear, fresh water? Or did it look like the contents of the black tank? If clear, it's possible that the supply line to your tank flush system just came loose and popped off its attachment point. If it looked like black water... then what popped off is likely a plumbing line associated with the flow into/out of the tank.

Fingers crossed it's the former!

Dan

Wednesday 9th of March 2022

Do you suggest to rinse every time we dump the black tank or is it good enough to do it every 2nd, 3rd, 4th, x times?

Thanks!

TheRVgeeks

Wednesday 9th of March 2022

Hi Dan! We use the black tank rinse every time we dump, although we're pretty obsessive about things, so not necessarily a requirement. We just figure it's a good idea to prevent things from building up in there!

Ken

Sunday 27th of February 2022

I’m about to buy my first rv and I’m very confused on when do I use the main campsite dumping station? If I’m at a site with full hookups that includes water, electrical and sewage, then wouldn’t all my black water (sewage) just go down right at campsite? If so, what is need for going to dumping station? Sorry for probably a stupid question.

TheRVgeeks

Monday 28th of February 2022

Hi Ken! Congratulations on your upcoming purchase! You're absolutely right... dump stations are only needed when you're NOT at a full hook-up. Whenever you're fully hooked up (electric/water/sewer), you're basically connected to your own personal dump station! It's actually better than using a dump station in two ways: 1) No line at the dump station, so no waiting, and no worry about people waiting behind you, and 2) Since you'll have a hard/threaded connection to the sewer outlet at your site (vs simply sticking the end of the sewer hose into a dump station opening), there is almost never any odor when dumping black water at a full hook-up. Dumping gray water at a dump station is fine, but we try to dump black at a full hook-up whenever possible. A third benefit is virtually-guaranteed access to a threaded water spigot for the black tank flush system. (Not all dump stations have that!) One thing, in case you weren't aware.... NEVER EVER leave your black tank valve open the whole time you're camped at a full hook-up! The black valve must remain closed except for during dumping. That's because all the "liquids" would run out while the "solids" remain in the tank, forming a nasty pile over time. That's called "pyramiding" and is one of the most awful newbie mistakes that a new RVer could make!

Duckiemoto

Thursday 23rd of December 2021

Hello, in your video you put ridX in your black tank. I've been told this is bad to do. Can you explain why you use this product. I appreciate all the knowledge my wife and I have learned from y'all.

TheRVgeeks

Friday 24th of December 2021

Hi, and thanks so much for the comment and question! Rid-X is fine in an RV tank, but if you'd like to use the Rid-X version specifically made for RVs, that should provide some extra peace of mind: https://amzn.to/3emSOuv

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