Should I Leave My Black Tank Open Or Closed? (RV Waste Tanks Guide)

RV Waste Tanks: Gray Tank vs. Black Tank

Most RVs have at least one gray tank and a black tank, as well as a fresh water tank. While the fresh water tank is a holding tank for clean water to be used for flushing, washing hands etc.

The gray tank is a holding tank for dirty water (from sink and shower).

The black tank is the holding tank of all human waste and water that is used for flushing the waste down the toilet. This also includes any RV toilet chemicals and RV toilet paper, when applicable.

RV Waste Tank

Four Reasons Why You Should Leave Your Black Tank Valves Closed

You should leave your black tank closed for several reasons:

  1. Environmental and sanitary issues (only “dump” human waste into appropriate sewer outlet)
  2. Backflow of gasses: if you leave the black tank hose attached AND open at an RV park etc. The sewer gas has open access to travel through the hose.
  3. Sewer flies etc. Similar to the gasses, same concept, but different nuisance. (Fun note: this can get even more serious in places like Florida)
  4. You need to have liquid waste accumulating in the black tank to avoid the “poop pyramid” buildup of solid waste drying and piling up.

When Can You Open Your RV Black Tank?

Despite the above list, some people prefer to keep their black tank open (or they just don’t know better yet until they have an expensive repair bill). That being said, when is it OK to open your black tank?

  1. When you are staying at an RV park with full hookups. This means the RV park has water, sewer and electricity for your RV to hook up to. I would still advise to only dump the black tank when it’s at least ⅔ full.
  2. When your black tank needs to be emptied and you locate a dump station. There are apps and RV GPS that show the nearest dump station. Also, many state parks and some RV parks have a dump station to use for a nominal fee for non-guests (usually $10 or so). Some gas stations have a dump station, as well.

When it comes to gray tanks, some people prefer to leave them open, especially if there are several occupants who take long showers and they want to avoid overflowing the gray tank.

When you arrive at a full hookup RV park, make sure your RV is within reaching distance of the sewer outlet, as well as the water and electric hookups. Locate the outlets prior to backing in and have enough slack in the sewer hose, as well as for the water and electric hookups.

Connect the sewer hose to the RV tank outlet. Most people have a clear 90-degree elbow, as well, that they place at the sewer ground opening. The connection should be solid, else secure/weigh down the hose connector with a rock to avoid spills. Some RV parks also have a heavier metal lid to secure the connection and to close the sewer hole when not in use.

Once the sewer hose is attached to the ground sewer opening, you can open the gray/black tank valve to empty the tank.

The rule of thumb is: BLACK BEFORE GRAY.

Be patient as the tank emptying can take a bit. If needed, backwash/flush the tank. Once there is minimal flow, close the tank. Add some water either via hose setup, with a bucket into the toilet or by flushing the toilet several times. Add RV toilet treatment, if desired.

How Long Does It Take For A Black Tank To Fill Up?

The black tank usually lasts anywhere from 2 days to almost a week, depending on capacity, usage and number of occupants. You should empty your black tank every 3-5 days, or when it is ⅔-¾ full.

While every new RV comes with amazing RV sensors that are supposed to indicate how full each tank is, most RVers agree that the sensors stop working fairly quickly and it can be nearly impossible to get them to work again, even when backwashing/flushing the black tank.

The reason for this is that any waste or TP etc can get stuck on the sensor at some point in time, giving a false positive reading.

You do not ever want to overfill your black tank, as it is one of the most unpleasant things that can happen to you as an RVer. Human waste will find a path of least resistance to flow out, usually out of a toilet, but sometimes onto the RV flooring. However, in worst case scenarios, it can actually damage your black tank, causing costly repairs and nasty cleanups.

Where To Dump Your Black Tank

There are many places where you can safely dump your waste. When at home or at a residential area, you can dump your waste into your sewer (there should be a sewer cleanout port to connect to). If you are moochdocking at someone’s place, make sure to check with them first to OK.

When boondocking without hookups, you can either use a “honey wagon”, which is a portable black tank that you can haul to a dump station to empty, or you can locate a gas station or RV park with a dump station. Apps like Campendium or Sanidumps can help you locate a dumps station near you.

Ideally, you dump your waste at an RV park that has either full hookups or a designated dump station. For non-paying guests, there’s usually a nominal fee to fill up your fresh tank and to use the dump station.

You should empty your black tank when it’s ⅔-¾ full, or every 3-5 days.

RV Waste Tank

Best RV Black Water Tank Treatments

With a little regular TLC for your black tank you can avoid costly repairs and smelly frustrations.

Here are the most important tips:

  1. Double-flush (water is crucial in disintegration of solid waste and TP).
  2. Use RV tank treatment (tabs or liquid, such as RST Max, Portapak or RV-Digest-It).
  3. Only empty the tank when ⅔ full to avoid buildups.
  4. Backwash/flush the tank monthly or every other month.
  5. Use RV toilet paper.


Can you put Pine Sol in an RV black tank?

Some RVers swear by it for odor control, although there are many other products one can use. Plus, not everyone likes the smell of Pine Sol.

What is RV black tank flushing?

Black tank flushing is regular deep clean maintenance on your black tank. This should be done once a month or every other month, depending on use and weather etc. Some RVs have a back tank flushing mechanism, some individuals use an RV wand to clean the black tank walls thoroughly.

Do you have to dump your own black tank?

Usually, yes. Unless you pay someone to do it or the RV park you stay at offers “honey wagon services”, you are IT. It’s not that bad, though, honestly, if you know what you are doing.

Should you leave water in your black tank when not in use?

This depends on how long you leave the RV standing unused. If you leave the RV unoccupied for more than 2 weeks, you should just empty all tanks and sanitize to avoid smells and growth of bacteria etc.

Can you drive with a full black tank?

Can you do it? Sure. Should you do it? Unless you are heading to a destination to dump the tank, it makes little sense to travel with a full black tank. 1. You cannot use the bathroom along the way. 2. You drive around with unnecessary waste weight, literally. 3. The added weight on the black tank, along with the vibration and stress of travel can lead to black tank damage, or backflush into your toilet.

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