RV Black Water Tank Dumping: Mistakes and Tips

RVing builds great memories. Some memories are great and last a lifetime. Some are not so great. RV Black Water Tank Dumping isn't a great memory, but when things go wrong, it's a lasting memory.

A New RV and a Bad Experience

Let me tell you a story. It’s about a couple who bought their first travel trailer. They had camped many times with family and friends. Watching them, they all seemed to know exactly what to do and when to do it. So how hard could it be? Like many things in life, there’s a huge difference between watching and doing.

The couple took their new trailer out right away. And things went wrong as soon as they reached the campground. The camp had fresh water available but they only had a 25’ hose. And it wasn't long enough to reach the water supply.

It was time to get another fresh water hose. It’s a hose, they thought. How hard could it be to find one? A quick trip to one hardware store followed by visiting another and then another ended up with no hose. They finally found a store with a freshwater hose. Problem solved.

Several hours later, they filled their trailer's fresh water tank.

Black Water Tank Dumping Disaster

After a week of happy camping in their new trailer, it was time to head home. Before hitting the road, they needed to dump their black and gray water tanks. And then they realized they hadn’t brought any rubber gloves Not a big deal. They would be careful and it wouldn't be a problem. They’d remember to get them before the next trip.

When they picked up their new trailer, the dealer showed them the basic operation of the trailer. The trailer looked ready to go. What they weren’t told was the valves on the black and gray tanks were open.

The dealer told them to dump the black water tank first. Without thinking to check the valves, the husband twisted the cap to the black water tank drain. The cap blew off into his hands. Black water flowed like water out of a fire hydrant. Covered from the knees down with … you get the idea, he closed the valve. He then connected the drain hose and emptied the tank.

We were that couple.

Some memories last a lifetime.

Here are a few things we’ve learned over the years about black water tanks.

Close the black water valves after dumping

If toilet paper gets stuck in the valve, it won’t seat. Sewage can fill the drain pipe. You won’t know until you remove the drain cap that sewage is going to spill. So you should always wear rubber gloves when dumping your tanks.

Tip #1 - Keep a box of rubber gloves on board. We keep ours with our tank dumping hoses.

Dump your black water tank when it's about 3/4 full

We are full-time Rvers. Because there are the two of us, we know our black water tank will be about ¾ full in about a week. And we’ve found that if we dump the tank when it’s less than half full, it doesn’t clear as well as when it is at least 3/4 full. If the tank is less than 3/4 full, we fill it the rest of the way with clear water.

Tip #2 - Make sure the black water tank is at least 3/4 full before dumping

2-step black water tank dumping process

We use a two-step process with the black water tank. We first make sure it’s full enough to empty. Once the tank has drained, we attach a garden hose to the black water flush inlet on the outside of the trailer. We then turn on the water to flush out any remaining debris in the tank.. We have a clear connection to the receiving tank so we continue flushing until we see the water is flowing clear which usually takes 2 or 3 minutes.


After dumping, we always shut and open the drain valve 3 or 4 times to make sure the valve shuts tight.

Treat the black water tank with deodorizing chemicals

Tank deodorizing chemicals have two purposes. First, they help keep the tank from smelling. Second, they help toilet paper dissolve.

Tip #3 - Add 3-5 gallons of fresh water to the black water tank then add deodorizer.

Do-it-yourself versus commercial black water tank deodorizers

There are DIY deodorizer formulas that you can find on the web. We've tried them, but we haven't found anything that works as well as a manufactured product.

Don't leave the black water tank valves open

RV tanks need draining pressure to clear debris. If the black water tank valve is open, there is no flushing action. Debris will accumulate. Over time, it will cake to the bottom of the tank. This has happened to a lot of people who thought an RV toilet operates like a home toilet. Over the years, we’ve seen it happen to campers, and it was not a good experience getting that mess cleared out

Tip # 4 - Keep the black water tank valve closed until it's ready to dump

Black water tank sensors

If there is one thing that is frustrating about RVing, it is the tank status display. Hard water deposits, toilet paper, and other debris can cause the indicator lights to foul. When it happens, we're left either thinking the tank is full or that it still has plenty of room. The solution is to shut off the water pump and open the toilet valve. You can see if the tank is ready to dump.

Tip #5 - Don't trust the tanks status lights

Black water tank hose management

To manage our hoses, we use two plastic see-through tubs, one for the dumping hoses, and the other for clear water. For safety, don't store the black and freshwater hoses together.

Tip #6 - Keep your black water and drinking water hoses separate

Dump the black water tank first

When we dump our tanks, we always dump the black water first then we dump the gray water. This allows the gray water to scrub any remaining debris from the dumping hose.

Tip #7 - Dump the black water tank first, then dump the grey water tank


That’s it for RV black water tank dumping. For the most part, it’s a simple process to get the tanks dumped and cleaned.

It isn't fun, but it’s all part of camping.

Back to Blogs

Leave a comment

Please note, comments need to be approved before they are published.

Amazon Affiliate

Clicking an Amazon link does not obligate you to making a purchase. As an Amazon Associate we earn a small commission from qualifying purchases at no added cost you. Read our full Disclosure Policy.