Guide To RV Holding Tank Sizes

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By Kelly Beasley

Is the size of your RV holding tanks essential to know? It most definitely is if you ever decide to camp without hookups.

The odds you will camp without campground hookups sometimes are pretty high. So yes, you should be aware of your RV waste tank sizes. This is the MOST important to know BEFORE you buy an RV.

SUV towing too large of a trailer

Why? Because if you are a camper who wants to dry camp a lot, you might regret buying a camper trailer with, say, a 10-gallon freshwater tank.

That RV is also not likely to have a large grey water tank or black water tank.

Therefore, your stay length is, for the most part, limited by your RV tank size. Sure, you can dump your waste tanks using a portable RV tank, but it's another chore to do while camping.

Best to have tank capacity that can accommodate your camping duration needs.

What Is The Average Size RV Waste Tank?

There is no one-size-fits-all when it comes to a typical RV holding tank size. They all vary.

You can probably figure out on your own that, on average, smaller trailers and motorhomes typically have smaller capacities.

Likewise, larger RVs tend to have larger RV waste tank and freshwater tank capacities.

Are there average sizes? Not really. Their capacities can vary wildly.

What Are RV Holding Tanks?

All RVs commonly come with these three RV sewer holding tanks:

  • Fresh water tank
  • Black water tank
  • Gray water tank

Here's a quick rundown of the purpose of each of these three tanks:

Fresh Water Tank

The fresh water tank holds the fresh/clean water you use for showering, washing dishes, and for when you flush the toilet. RV fresh water pumps push the freshwater through your pipes.

Black Water Tank

Camper black water tanks hold everything (liquid and solid waste) that goes down the toilet. It's the keeper of sewage/human waste.

How many gallons is a black tank? As many as the RV tells you it holds. RV black water tank size varies from RV to RV. The average RV black water tank size can vary from as little as 15 gallons to 60+ gallons. The larger the RV, typically the larger the RV black tank size.

Gray Water Tank

A gray water storage tank holds the waste water that goes down your sink and shower drains.

The RV black water tanks and gray tanks are made to hold all of your wastewater until you can get your RV to a dump station to dump your black and grey tanks. Emptying them is relatively easy.

The fresh water tank is the one that supplies the water that will end up in the two waste tanks.

Marshall's Rig Utah

What Is The Typical RV Holding Tank Size?

What size are RV holding tanks? Is there a typical RV holding tank size?

Though there may be an 'average' size for holding tanks on certain RV classes, you should not assume the tank capacity of any of your tanks or ANY RV you are looking to purchase.

There are no 'average' sizes of the three tanks. Remember, there are usually three different tanks!

And they rarely are the same size. Every RV has its own configuration, some requiring X gallons of water for drinking and washing, and others having a black water capacity that can suit a family of four.

Typically, the larger the RV, the larger the tanks will be. A smaller travel trailer will have, USUALLY, less tank capacities than a 40' Class A RV.

The smallest of RV classes, the Class B RV (van), typically has the smallest tanks. The 'Class A' motorhome tends to have the largest sized tanks.

Sometimes RVs even have two black water tanks or grey water tanks.

Suppose you are ever camping without connections to water and a sewer. In that case, it's best to have a general idea of your RV water tank size and its waste tank sizes and know how long you can go without having to dump (draining your waste using a camper septic hose) or refill.

Also, take into consideration how many people will be staying in the RV. The more users, the shorter your RV water tanks and waste tanks will last.

Where Do I Look For RV Tank Sizes?

You might find the size of your black water holding tank and grey water tanks inside the RV. It might be on a piece of paper attached to the inside of a cabinet somewhere.

This paper also might tell you other details about the appliances in the RV, such as your refrigerator, stove, and furnace.

If not there, check your owner's manual.

If your RV came without an owner's manual, go online and look it up there.

Simply Google search your RV brand, make, model, and year and 'tank sizes.'

You may be able to find the brochure for your year and model RV which should indicate the RV tank capacities.

Trixie dog lying down in front of Kelly's RV outside of Glacier

How Do I Read The Three Tank Size Numbers?

The gallon capacities of the three tanks might be written something like this in your RV:

40-35-28 => Fresh-Grey-Black

So you have a 40-gallon fresh tank, 35-gallon capacity grey tank, and a 28-gallon capacity black tank.

The order of these is always the same. So try to remember from left to right, the same way you write. Starts clean and ends up dirty!

Clean on left, dirty on the right, beginning to end.

What Size RV Holding Tank Do I Need?

Keep in mind that almost every RV has THREE holding tanks - One to hold fresh water, one that holds toilet sewage, and one that catches drain water.

How much cooking you do, how much water you use, how many people are using the RV... these are all factors to consider when figuring out how large your tanks should be.

It's entirely possible for a family of four to make it a week on all three tanks IF THEY ARE CONSERVATIVE, minimize their water usage, and don't have small tanks to start with.

Also, there are ways to dump the waste and refill the fresh water without moving the RV.

But if you have to do so every three days or so, this is a great way to make a relaxing vacation not so relaxing.

The larger your tanks, the better. Especially if you are RVing with more than two people.

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How Large Is An RV Water Tank?

RV fresh water tank size range anywhere from 20 gallons to 100 gallons. A smaller RV will (typically) have a smaller freshwater tank.

Larger RVs tend to have a larger tank size for fresh water, but this isn't always the case. If you are purchasing an RV, DO NOT assume tank size based on size of the actual RV. You might be shocked to find that the relatively large recreational vehicle you are looking at has a relatively small tank capacity.

Find out if it has larger holding tanks or smaller holding tanks. If you NEVER dry camp, the average size of your tanks doesn't matter.

How Big Of A Grey Water Tank Do I Need?

Again, how large of a grey water tank you need depends on how often you want to dry camp. It also depends on how long you want to stay at that spot.

Most boondocking and dry camping spots have a stay limit, usually on average, of two weeks. Therefore, you don't need any tanks that can go longer than that.

But honestly, if you want to dry camp a lot then RV grey water tank size becomes important - the larger the tank, the better. SOME RVs come with two gray water tanks. Much more capacity there.

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

First of all, know that you should never leave the black tank valve open if you are connected to a sewer. This will undoubtedly cause an eventual clog via the infamous poop pyramid.

Leave it closed until almost full (might take a week or more), then open the valve to dump (when at an appropriate dump facility). Immediately close the valve again until full.

Otherwise, if you are NOT connected to a sewer via a sewer hose, how long it will take to fill is dependent on a few variables, such as:

  • RV black water tank capacity.
  • How many people are using the toilet?
  • If you are flushing TP down into the toilet (this takes up more space in the black tank).
  • If the males are peeing into the toilet or outside.
  • How much water you put into the bowl before flushing.
  • How long you flush the toilet.

You could do very long flushes and fill up the toilet in a few days. Or you could be very conservative; guys pee outside, no TP down into the tank, and go for a few weeks (if your RV black tank capacity is large enough).

It all depends. It's best to experiment with this while parked at a campground with a sewer connection.

To experiment, use the toilet as you would while dry camping, and figure out how many days until your sensors read full. Then you can dump, do it a few more times, and take the average. And there's your answer.

I can go just over two weeks with how conservative I am with my toilet usage. My tank is about 27 gallons. My fresh water tank size is 20 gallons. I can also go two weeks with extreme conservative usage.

Marshall has a 45 gallon black tank (all his tanks are 45 gallons) and can go close to a month if he pees a lot outside.

Couple sitting in front of 5th wheel at rv park

How Long Can A Gray Water Tank Last?

Well, say you have and want to use a washing machine while dry camping, and have a big family that uses a ton of water.

Don't expect to go more than a few days, no matter how big your gray tank is.

My gray water tank storage capacity is pretty tiny - about 27 gallons, and I can easily go for two weeks without having to dump.

It's all about your decision of how much to conserve or not to conserve.

If you can't go as long as you want to stay, if there's a dump station nearby, OR you have the capability to lift an extremely heavy portable waste tank into the back of your pickup truck, you could empty at least part of the tank using a waste hose and rubber gloves.

Then you can go dump it without having to move the RV.

How Do You Know How Full Your Tanks Are?

Sensors make it very easy to see how full your RV tanks are. Most RVs come with built-in sensors that gauge your levels for you. Simply press a button, and the RV tank level indicator tells you how close to full or empty the tank is.

Some people can visually see their freshwater tank and see how full it is, most often in travel trailers.

Others can look right down into their black tank when they flush and see how full the tank is becoming.

Your RV toilet tells you when the black tank is about to be full to the brim. It will 'burp'... something you will quickly learn by ear.

When it does the burp, you only have a few flushes left before the black water tank backs up into the toilet bowl.

The gray tank, once full, will start to back up into the lowest outlet of the plumbing systems, usually the shower drain.

You don't have to let them go this long before you know you're full. Your sensors, if working correctly, will monitor and let you know your waste tanks are about to be full or empty (fresh water)!

Once they are, it's time to look for dump stations in the area.

Airstream RV exterior at Alabama Hills


Your RV comes with three tanks. A gray water tank, a black water tank, and a fresh water tank for drinking water and for cleaning dishes and bodies.

They rarely all have the same size capacity. Some have larger tanks, while others have smaller tanks.

Usually, the fresh water tank is larger than the other two tanks. Smaller campers have smaller tanks, while the RV holding tank capacity of a larger RV will typically be higher.

To find out the size of yours, check the owner's manual, or look it up online. Sometimes the sizes are displayed on an information sheet attached to the inside the RV somewhere.

How large of these tanks you need depends on many things - how well do you conserve water? Are you willing to take navy showers? And will you be connected to a sewer system most of the time? Will you have a water hookup?

If you want to dry camp at all, be aware of the sizes of your black and gray water tanks. If you are buying an RV, DO NOT OVERLOOK the holding tank size of any RV you are interested in.

The more tank capacity you have, the better! It can't hurt, right?

How many gallons does an RV hold? As mentioned above, it depends on the size of the tank, which can vary considerably between makes, models, and floor plans.

Kelly Headshot

I dedicated myself to living the full-time RV life for over 6.5 years, immersing myself in the unique quirks and joys of the boondocking lifestyle and gaining a wealth of knowledge and experience along the way. In December 2020, my business partner and I made the transition to part-time RVing, but in January 2023, we hit the road once again, this time in our trusty vans. My mission is to help others embrace the RVing lifestyle with confidence and excitement, armed with the knowledge and resources needed to make the most of their adventures. I believe that the more you know, the more you can truly appreciate and enjoy the freedom and flexibility of the open road.

  • If I want to use my camper for a tailgate and there are 40 people- will I be okay you think? Obviously not everyone will use it. But in a 3-4 hour period several might. Thoughts?

    • Hy Cryss-

      It all depends. We can’t tell you for sure without knowing what you have. What type of toilet is it? Cassette? Composting? Or do you have a black tank? And what size is the black tank?

      If you don’t know, how long is the trailer? It’s most likely you have something pretty common- a toilet with a black tank.

      And most black tanks are at least around 20 gallons. (For instance, my old 24′ travel trailer had about a 20 gal black tank.) So unless you have a teeny tiny trailer (under 20′) you’ll probably be fine starting with an empty tank.

      Be VERY CAREFUL about this one thing though- if the guests don’t use enough water/use too much toilet paper, they could clog your system. I would NOT let them put the used TP down the toilet.

      You can put a garbage can with a lid in the bathroom and instruct guests to put the used TP in there.

      If you have a cassette toilet, same thing. And note that a cassette toilet only holds just under 5 gallons. That’s not much. So figure out what you have and you will have better piece of mind as to whether your party may become a s*** show or not LOL!! Have fun!

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