rv holding tanks open or closed?

So, you got that campsite with full hookups and you’re so excited about it! Or your permanent seasonal site has full hook ups and now you never have to worry about pump outs again! So exciting…we know the feeling! It’s one of those great luxuries of RV camping.

But, the question that seems to come up all the time is…Do I keep the RV holding tanks open or closed when hooked up to sewer?

I get it, we’re on a full hookup site, why close the holding tanks and keep all that “crap” in our waste holding tank? Let it flow baby! Why is this even a question?

Well, not so fast.

The best option is to keep your RV holding tanks closed until more than halfway full. We’ll Explain.

Why Keep Your RV Holding Tanks Closed on Full Sewer Hookup?

Best RV Sewer Hose

I know. Closed? Isn’t this defeating the purpose? We have a full hook up site. We don’t have to worry about our holding tanks filling. Let’s connect our sewer hose and let it flow! We can use all the water we want. Take those long hot showers because we have a tankless water heater and won’t run out of hot water! Use the bathroom without worry!

Unfortunately, keeping the holding tank closed until more than halfway full is the best option.


There are a lot of reasons why this makes sense. Read on…

Why Keep the Waste Holding Tank (or Black Tank) Closed?

This is the big one. The Black tank. The waste holding tank. The one no one likes. The one that everyone talks about. It’s got your number 1 and your number 2 in there. Yuck.

So why are we saying to keep your waste holding tank valves closed?

There are a lot of problems that can come with keeping them open and letting it “flow”.

Leaving the black waste holding tank open will slowly allow your waste holding tanks to drain. Slowly being the key. And in some cases, not all of the waste will make it out.

What’s coming out of those RV waste holding tanks is your number 1, your number 2, toilet paper and a little bit of water.

With this, there certainly isn’t enough liquid to have it flow out. Plus, the waste hasn’t had time to break down in the waste holding tank.

You know how we add those waste holding tank pods? Yes, it helps prevent some of the smell, but it also breaks down the waste and toilet paper so when you open the tank to dump it, it all flushes out in the water, ideally no chunks.

So when you leave the RV waste holding tank open, some drains, mostly the liquid, and then your toilet paper which hasn’t broken down and your number 2 which hasn’t broken down gets clogged up along the way.

This can cause the dreaded “poop pyramid”. It’s a build up of poop and toilet paper that creates a blockage in your waste holding tank so you can’t dump your tank.

Not Good.

Without the extra water to flush out at a rapid pace and take all the waste with it, you are subjecting yourself to black waste holding tank build-up. This will stop any good flow from happening, even when you have it closed and go to a dump station.

And to remove it is quite the process. If you can. If not, replacement tanks are in your future. So this should be enough to convince you to close those tanks and dump when more than halfway full. That will allow enough water pressure to flush it all out and allow time to decompose.

Still not convinced?

Another reason to keep it closed is drain flies.

Drain flies are a common pest that can be found in rv holding tanks. They are attracted to the smell of rotting waste, and they can quickly infest your holding tanks if they are left open. If you see drain flies in your RV holding tanks, it’s important to take action to get rid of them.

The best way to get rid of drain flies is to dump your tanks and clean them out properly. Make sure to remove all of the waste and flush the tanks until they are clean. You may also want to use a pesticide to kill any remaining flies.

Once you’ve cleaned your holding tanks, make sure to keep them closed until you’re ready to dump them again. This will prevent the flies from coming back and infesting your tanks again.

Last, the smell. Sometimes the smell from the RV septic tanks system can work its way back up into your camper. Yeah, gross. So keep them closed to prevent that horrible smell.

Hopefully, these are enough reasons for you to keep your RV holding tanks closed when connected to full hookups at your campsite.

What about the Gray Tank?

This one can be a little bit more of a “gray” area. It’s not as “black” and white and keeping your waste holding tank closed.

I still prefer to keep the gray tank closed when connected to full hook up. I just see it as I will need to go out and dump the waste holding tank for all the various reasons above, so why not just pull the gray as well.

Plus, it does provide a rinse when you do it AFTER you dump the waste holding tank.

Another reason I Like to keep the gray tank valve closed is for some of the food particles that might make it down the drain in your sink, or some of the hair and residue that may go down the shower drain. Same idea as with the waste holding tank. The more water that builds up in the RV holding tank while closed will provide greater pressure and flow when you dump taking all that debris out with it.

To me, it keeps it cleaner and prevents any other build up.

What is the Waste Holding Tank or Blank Tank on an RV?

RV Black tank treatment

The waste holding tank or black tank on an RV is the tank that stores the black waste water. This is the holding tank that collects the waste from the camper, and it needs to be emptied regularly.

What is the Gray Water Tank on an RV?

The gray tank on an RV is the tank that stores the gray water. This is the wastewater from the sinks, showers, and washing machine, and it needs to be emptied regularly.

How to Flush the Waste Holding Tank on an RV?

Flushing the waste holding tank on an RV is a simple process that only takes a few minutes. First, make sure that the dump valves are closed and the tank is empty. Then, fill the black tank with water until it’s about halfway full. Add a quart of dish soap or waste holding tank treatment to the tank, and let it sit for about 15 minutes. If you are mobile, drive around with it filled up so it splashes around the tanks to clean them better.

Next, connect your sewer hose to the sewer and open the dump valves. The dish soap will help to remove any residue or build-up in the tank. Let the water drain and then you can start to flush the tank with fresh water.

Connect a hose to your black tank flush if you have one. Make sure you use a hose that will only be used for this purpose.

If you don’t have a black tank flush valve, insert the hose into your toilet. Let the freshwater run until it’s clear exiting your camper.

You’re now ready to continue using your RV!

What Type of Sewer Hose Should I Use to Dump My RV Tanks?

RV Sewer Hose

When it comes to dumping your RV tanks, you want to use a sewer hose to do the job. This is a specialized hose that’s designed for emptying RV waste-holding tanks, and it will make the process much easier. You can find sewer hoses at most RV stores, or online. Read our article about the top 5 RV sewer hoses.

Make sure to get a dump hose that’s long enough to reach the dump valves on your RV. The standard length is about 10-15 feet, but you may need a longer hose if your RV is parked in a tight spot. Always check the length before you buy, to make sure it will be long enough for your needs. You can typically add extensions if needed.

When using the sewer hose, make sure to keep it sloped downwards. We love using a sewer hose snake to help with this. This will help the wastewater flow out of the tank, and into the dump station. Never dump water uphill, as it will back up into your tanks and cause a mess.

Finally, always dump your tanks in designated dump stations. Never dump them into a body of water, as this can contaminate the environment. Follow tips to avoid dump tank smells and protect the environment!

We also recommend using an RV Black tank treatment to help break down the waste.

How Do I Dump My RV Holding Tanks?

RV Dump Station

Dumping your RV holding tanks is a pretty simple process, but there are a few things you need to know in order to do it correctly.

First, make sure that your holding tanks are indeed full by checking the level indicators on the side of the tank. Once you’re sure they’re full, connect your sewer hose to your RV dump outlet and the other end into the campground sewer outlet or into the dump station’s outlet.

Next, find the dump pull valve – it will be a black or gray handle sticking out by the side of the tank. Start with the black first!

Once the black has finished, be sure to close the tank. Then you can proceed with opening and draining the gray water tank.

Doing the gray tank last allows that water to clear out any leftover wastewater that ran through your dump hose.

When you’re done, be sure to close the dump valve again to prevent any leaks.

Should I Use a Waste Holding Tank Treatment?

There are a lot of different types of RV waste holding tank treatments on the market, and it can be a bit confusing to decide which one to use. Some people swear by them, while others say they’re not really necessary.

I always use them!

They help with the smell and help break down all that waste. To me, it’s worth the small investment in buying the waste tank treatment.

In the end, it’s up to you whether or not you want to use a waste-holding tank treatment. But if you do decide to use one, be sure to follow the instructions on the bottle carefully.


When it comes to dumping tanks on a full hookup site, there are a few things to keep in mind. It’s important to keep the dump valves closed until ready to dump and to use a dump sewer hose to make the process easier. You should also dump your RV holding tanks in a designated dump station, and never dump them into a body of water. Finally, you may want to use an RV waste-holding tank treatment to help with the smell and waste breakdown.


If you’re lucky to have a full hookup site, it’s important to keep your RV holding tanks closed until ready to dump. This will help prevent any leaks or spills, prevent blockage, and make the process much easier. You can find sewer dump hoses and black tank treatments at most RV stores, or online. Always dump your tanks in a designated dump station – never dump them into a body of water!

Thanks for reading!

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