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  7. An Easy Guide to RV Holding Tanks

An Easy Guide to RV Holding Tanks

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No matter how much fun you’re having in your RV, eventually you’re going to miss one particular thing from home — a bathroom where toilet waste just disappears, never to be seen again. The trade-off for the privacy and convenience of a bathroom in an RV is regularly cleaning, maintaining and emptying the holding tanks. Done right, it doesn’t have to be a dirty job, and using the right chemicals will eliminate odors and keep the contents flowing without issues.

The black-water tank is one of three (or four) tanks in the typical RV. The others include a freshwater tank, which holds water for cooking, drinking and bathing, and one (or two) gray-water tanks, which is where the freshwater drains after it’s used in these aforementioned places. The black tank holds toilet waste; the toilet is usually mounted to the top of the black tank and empties directly into it or via a connecting pipe.

Obviously, the gray and black tanks need to be emptied regularly, but how and when you do it determines how well they drain. Solid waste can accumulate in the black tank and clog the drainpipe if insufficient water is present, but despite what you might think, emptying it sooner rather than later isn’t always the best idea. The rule of thumb is not to empty the black tank until it’s about two-thirds full; this ensures there’s enough water in the tank to flush away solids.

Hooking up the Hose

Dumping the holding tanks can be quick and easy, or an environmental disaster. Start by inserting the downstream fitting on the 3-inch dump hose into the sewer port. Use a dump hose with a right-angle fitting to connect the sewer port — it’s less likely to pull out or leak — and make sure it has threads or locking tabs to hold the hose secure and prevent leaks and odors. Be sure there’s enough sewer-hose length to reach the RV; you may need to connect several hoses.

Before dumping the black tank, make sure all the tank valves are closed. Next, remove the cap to the outlet pipe on the RV and attach the sewer hose’s bayonet fitting to the end of the pipe. Icky-but-handy dumping tip: Use a clear bayonet fitting at the outlet pipe on the RV so you can tell when the tank is clean and empty. Be sure there is plenty of water in the black tank. Once the sewer hose is securely in place, release the black-tank valve.

RV Toilet Tips

• When pouring water or tank treatment down the toilet, turn off the exhaust fan in the bathroom momentarily so it doesn’t draw odor from the black tank up into the living quarters.

• Use only toilet paper made for RV and marine waste systems. It’s designed to break down easily and not plug up the system.

• Leave the black- and gray-tank drain valves closed in camp. Keep an eye on the levels and drain when needed. If the black tank is allowed to drain constantly, there won’t be enough water to keep solids flowing when you need to empty it, which can lead to buildup and even plugging of the system.

• Always empty the black tank first, then the gray tank, which flushes out the sewer hose.

Black Tank Flush

Once the black tank is empty, flushing with water will clean away contents that did not flow out naturally. This can be done a number of ways. A clean-out wand (available at Camping World and other RV-accessory stores) can be attached to a water hose designed for gray water (never use the freshwater hose) and used to force water down through the toilet valve. If a hose is not convenient, pouring a bucket or two of water down the toilet to finish flushing the tank will help.

The more effective method is to use a tank flusher that’s built into the tank. Many manufacturers are providing these clean-out systems; it’s also possible to install one using an aftermarket kit, providing there’s access to the tank. When using the onboard tank-flushing apparatus, make sure the tank drain is open to prevent the tank from overfilling and/or rupturing. Do this last step at least twice. And, again, use a hose dedicated for this purpose, not the freshwater hose. Seasoned owners will fill the tank with freshwater at least once and drain again to make sure the contents are cleared out properly. Use caution if the tank is filled with water via the built-in flushing port, and never become distracted while performing this task.

While some owners keep the gray-tank valve open while hooked up, the preferred method is to allow the tank to fill before draining. This allows the tank to flush thoroughly when dumping, and the water can be used to flush the sewer hose after dumping the black tank. The black-tank valve must be closed before dumping the gray tank.

When the dumping chores are finished, rinse off the area around the dump station. After everything is cleaned up and stowed away, there’s just two more steps: add water to the black tank, at least 3 or 4 gallons, and add a holding-tank treatment to break down solids and reduce odors.

Breaking Down the Contents

Holding-tank chemicals all do pretty much the same thing — deodorize the contents of the tank and break down solids so they’re easier to flush — but they go about it in different ways. Bacterial treatments do it all: they break down waste, which keeps it from clumping and clogging, and control odor, but they start to lose their effectiveness at temperatures above about 85 degrees Fahrenheit.

Enzyme treatments use proteins to break down waste and prevent residue from forming inside the tank. But they don’t do anything to control odor, so most enzyme treatments are mixed with strong scents that either cover up the tank’s natural smell or replace it with another one that is just as annoying, depending on how you feel about the inside of the RV smelling like the perfume counter at a department store.

Some people prefer to use conventional chemicals that have a long track record for reducing odors and breaking down contents. The use of formaldehyde is controversial, and although very effective, in some areas it’s prohibited. Mixing household cleaners in a holding tank that’s been treated with RV-specific products can create dangerous chemical reactions.

Holding-tank treatments come in several forms, including powders, drop-in packets and liquids. The formula matters, not the form, so pick the one that’s most convenient and treat the RV’s holding tank after every dumping.

Here’s a roundup of popular holding-tank treatments that the manufacturers claim will make you miss the bathroom at home a little bit less and make the one in your RV homier.


TST Max and MEGA sewage drop-in tablets tubs

TST Max Drop-Ins break down waste and tissue without using formaldehyde and contain a blend of hibiscus breeze-scented surfactant oils that trap odors. It’s ultra-concentrated and requires just one drop-in to treat an entire 40-gallon tank. Mega Drop-Ins digest waste and tissue, and clean sensors and tanks without using formaldehyde. The quick-dissolving packets come with a 20 percent stronger deodorizer in lemon or coastal breeze.

Century Chemicals

Travel Jon Blue Max toss-in packets

Travel Jon Blue Max toss-in packets are biodegradable and contain no formaldehyde. They combine a powerful effervescent cleaning action with maximum odor-fighting power. One packet treats a 40-gallon tank and lasts up to a week to help break down tissue and waste. Travel Jon Waste Digester is a more concentrated formula that costs less to use, uses enzymes to break down waste and control odors, and can be used in black and gray tanks. The non-staining powder contains no formaldehyde and comes in 2-ounce pouches.


Drop-In Bowl Cleaner & Tank Treatment

According to Dometic, its 3 ’N 1 Drop-In Bowl Cleaner & Tank Treatment is the ultimate in convenience for cleaning a mobile toilet and treating the waste tank. Special enzymes help to neutralize tank odors while the product’s bubbling action works. One rapid-dissolving drop-in is good for 40 gallons and releases a lavender scent. Clean ’N Green Holding Tank Treatment keeps the tank’s interior clean and has a fresh scent. Both products are 100 percent biodegradable.


Eco-Save Original Formula

Eco-Save Original Formula is a cleaner and odor remover that’s said to be safe for all RV holding tanks. To treat the typical tank, 3 to 4 ounces of the mild, perfumed treatment is sufficient. A quart bottle treats a tank eight or nine times. The Fragrance-Enhanced Eco-Save has a cherry scent. Eco-Save Dry is a concentrated bacterial non-perfumed dry mixture containing a surfactant to lubricate the valves. Perfect for long periods of boondocking, one jar treats 30 to 35 tanks, and works in both black and gray tanks. Select campgrounds and dealers carry Eco-Save, and it’s available for less money than directly through the company.


Kronen Nature Safe liquid

Kronen Nature Safe liquid is formaldehyde-free and comes in a 32-ounce tip-and-measure bottle. It’s formulated to destroy odors on contact and uses naturally occurring microorganisms to liquefy waste and tissue. Kronen Nature Safe Drop In’s come in a pack of 10 and use the same microorganisms as the liquid to break down waste and tissue and deodorize the tank.


Oxy-Kem from ARC Products

Oxy-Kem from ARC Products is designed to clean and deodorize black and gray tanks, sinks, drains and sensors. It works up to five times better than chemical, enzyme or formaldehyde products, according to the manufacturer, and can treat up to 60 gallons of water. It’s said to be environmentally friendly and scientifically proven.

Star brite

Bio Odor from Star brite

Bio Odor from Star brite is effective at breaking down waste and mitigating odor over extended periods of time. The environmentally friendly treatment uses enzymes and is safe for all holding tanks. Instant Fresh is formaldehyde-free, biodegradable and non-staining, and uses the latest technological lubricants to keep drain valves from sticking. The fresh pine or lemon scent controls tank odors and breaks down waste quickly and efficiently.


TankTechsRx bottle

TankTechsRx comes in 8-ounce, 16-ounce and liter sizes and is formulated for use in black and gray tanks. It uses beneficial bacteria that multiplies to treat tanks of any size. The probiotic bacteria eliminates odor and breaks down waste to liquid. According to the company, the product’s living microorganisms repopulate to continuously clean tanks.


Aqua-Kem Toss-Ins bags

Aqua-Kem Toss-Ins come in water-soluble packets that you toss into the holding tank. They dissolve fast and deliver effective cleaning and odor elimination. Tank Blaster is the first two-in-one RV holding-tank cleaner specifically for black, gray and portable tanks, according to Thetford. It uses an active enzymatic blend to blast crud and attack tissue, waste and grease.

Thetford Bio products

In response to a California law taking effect in 2022 that bans certain chemicals in RV holding-tank treatments, Thetford has launched a new line of liquid and dry solutions that are free of harsh chemicals, including formaldehyde and bronopol. Thetford claims its environmentally friendly, California-compliant AquaBio products effectively break down and deodorize holding-tank contents while being safe for RV tanks, toilets and septic systems. Liquid AquaBio is available in 8-ounce six-packs and 32-ounce, half-gallon and gallon bottles. Dry treatments are sold in tear-open packets as well as toss-ins that come in 16-count pouches and 30-count tubs. All have a citrus scent.


Odorlos Quick Dissolving Drop-Ins from Valterra products

Safe for all holding tanks and septic-tank systems and effective in extreme temperatures, Odorlos Quick Dissolving Drop-Ins from Valterra break down waste effectively and quickly in black and gray tanks. The nontoxic scent-free treatment is biodegradable and contains no formaldehyde while preventing clogs and odors. Available in liquid, powder and drop-in treatments, Pure Power Blue is a highly concentrated bio-active formula that breaks down toilet paper, waste, grease and soap scum in black and gray tanks. A 2-ounce packet treats 40 gallons and controls odors in temperatures up to 130 degrees Fahrenheit.


Porta-Por from Walex products

Porta-Por from Walex is a super-concentrated formula that breaks down waste and paper, and cleans holding-tank sensors. The formaldehyde-free, commercial- strength formula works in black and gray tanks, and provides weeklong odor control. Commando water-soluble drop-ins use an all-natural enzyme to break down waste, paper and residual buildup on the tank walls and sensor in as little as 12 to 24 hours.

Jerry Smith
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