What Size Portable RV Waste Tank Do I Need?

Size the tote by how you will move it full, not by how big your gray tank is. Waste weighs roughly eight pounds per gallon, so a 21-gallon tank is around 170 pounds loaded and a 36-gallon tank is in the region of 300. If you are pulling it by hand, 21 gallons is the sensible ceiling. If you will tow it slowly behind a vehicle or a cart on four wheels, 32 to 36 gallons saves you trips. Buying more capacity than you can move is the most common mistake in this category.

Part of our sewer and water guide. Which specific tank to buy is in the portable waste tank roundup; this page is the sizing decision that comes first.

Start with the weight, because everything follows from it

Water weighs about 8.3 pounds a gallon and waste water is close enough to that for planning. Run the arithmetic before you shop and the question mostly answers itself.

Those weights are the capacity multiplied by the weight of water; they are arithmetic rather than a manufacturer figure, and the empty weight of the tank is on top. The point is not the precise number. The point is that the difference between 21 and 36 gallons is the difference between a tank you can handle and a tank that handles you.

Then count the trips you are trying to avoid

The reason to buy a bigger tote is to take a whole tank in one trip instead of three. So look up your trailer’s gray tank capacity in the owner’s manual — it is the bigger of the two tanks on most travel trailers — and compare.

A 21-gallon tote is roughly one gray tank on a small trailer and half a tank on a larger one. A 32 to 36-gallon tote takes a whole gray tank on most travel trailers in one go. If you are dry camping for a week, that is the difference between one walk to the dump station per tank and three.

If you are at a site with water and power but no sewer for a weekend, the smaller tank is almost certainly enough and far easier to live with.

Two wheels or four is a bigger decision than the gallons

This is the specification people skim and then regret, so it is worth being explicit.

Two wheels means the tank is a wheelbarrow: the wheels carry part of the weight and your arms carry the rest, the whole way. That is fine at 21 gallons on a paved road and unpleasant at 36 gallons on gravel.

Four wheels means the tank carries its own weight and you are only steering it. With a swiveling front pair it tracks where you point it. This is the single biggest usability difference between totes once they are full, and it is what the price premium on the larger tanks is mostly buying.

Pneumatic versus no-flat tires is the sub-decision. Pneumatic tires roll over grass and gravel far better; they can also go flat, and a flat on a loaded tote is a genuinely bad afternoon. No-flat wheels never strand you and never roll as well. Gravel sites favor pneumatic; a storage lot that sits all winter favors no-flat.

“Not published” means exactly that: the manufacturer does not publish the figure, so we are not printing one. Note the row that matters most for storage — the larger tanks are 45 to 51 inches long, and that length, rather than the price, is usually what sends people back down a size.

The storage question nobody asks first

A tote has to live somewhere for the 95 percent of the time it is not in use, and it is an awkward shape. Before you choose a capacity, go and look at the space.

Measure your pass-through compartment. A 45 to 51-inch tank does not fit in many of them, and if it does it has displaced your chairs, your blocks and your hose.

Check whether it will hang on the rear ladder. Several tanks are designed to, which keeps a compartment free — but the heavier tanks are a two-hand lift onto a hook, which is worth knowing before you buy one at 45 pounds empty.

Think about the truck bed. If it rides in the bed, look for tie-down grooves. A loose tote in a pickup bed is a projectile.

Pick by how you will move it

Pulling it by hand on a paved loop: 21 gallons on two wheels. Towing it slowly on gravel: a four-wheel 32-gallon tank with pneumatic tires. Nervous about overfilling: the 35-gallon tank with the level gauge. A full gray tank in one trip and somewhere to store 47 inches: the 36-gallon tank.

Best for A first tote for a travel trailer

Camco Rhino Portable Waste Tank (21 gallon)

The sensible first tote: big enough to be worth the trip to the dump station, small enough that a full one does not get away from you.

$209.00 - View on Amazon#ad we may earn a commission - price as of November 12, 2026

Best for Towing to the dump station

Barker 4-Wheeler Tote-Along Portable Waste Tank (32 gallon)

The tank to buy if you will be towing it rather than pulling it: four wheels take the weight and the 3-in valve means no tipping.

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Best for No overfilling and no tipping

Thetford Titan 4-Wheel Portable Waste Tank (35 gallon)

The most beginner-proof tote on the list: the level gauge stops the overfill mistake, and nothing ever needs tipping.

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Best for Long stays and bigger tanks

Camco Rhino Portable Waste Tank (36 gallon)

The right tank if you stay put for a week without a sewer hookup. Too much tank if you plan to pull it by hand.

$297.65 - View on Amazon#ad we may earn a commission - price as of November 12, 2026

What size to buy, in one paragraph each

Buy 21 gallons if this is your first tote, your sites are mostly full hookup with the occasional exception, you will be moving it yourself, and storage is tight. It is enough to be worth the trip and small enough that a full one does not get away from you.

Buy 32 to 36 gallons if you regularly stay several days without a sewer connection, you have a vehicle or cart to tow it with, and you have measured somewhere for it to live. Four wheels, and a level gauge if you can get one.

Buy nothing if your sites have sewer hookups. A tote solves a problem you do not have, and it is a large object to store for nothing. The small sewer accessories are a far better use of the same money.

Using one without making a mess

Fill it from the trailer with the tote on level ground. A tote on a slope reads as fuller or emptier than it is.

Dump black into it only if you intend to rinse it properly. Many people use a tote for gray water only and move the trailer for the black tank, which is a legitimate strategy.

Empty it with the valve, not by tipping. A horizontal three-inch valve exists so a full tank never has to be lifted on its end.

Rinse it out every time, through the washout port. A tote that gets rinsed is a piece of equipment. One that does not becomes something you avoid using, and then you have stored it for nothing. Use a dedicated rinse hose, never the drinking water hose.