Dave Solberg

RV Black Water Tank Overview

Dave Solberg
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Duration:   3:11   mins

It is important to understand how to properly empty your RV waste tank system, including knowing the difference between the two tanks and compiling the hoses and tools that make your visits to the dump station easier. In this free lesson, RV expert Dave Solberg conducts a quick overview of the RV waste tank system on his demo basement model vehicle, explaining the proper technique for safe dumping at any campground or city facility and introducing any tools you might need throughout the process.

RV Waste Tank Basics

RV wastewater tanks are classified as black water and gray water systems. The black water tank valve can typically be identified as the larger valve, usually 3 inches in diameter, while the gray water tank valve is smaller, usually 1.5 inches in diameter.

Toilets on an RV are always connected to the black water system, which contains sewage from personal waste. Other water drains onboard are connected to the gray water waste tank, which holds less hazardous water from such sources as sinks and showers. However, depending on the layout, some manufacturers will have the system set up in such a way that the sinks dump into the black tank, but in most vehicles the black water tank will be filled with primarily sewage from the toilet.

Even though the gray RV waste tank holds cleaner waste than the black water tank, you still do not want to dump this tank into the open. Both tanks should be properly emptied at designated dump stations, using equipment that allows for safe and clean dumping.

How to Dump an RV Waste Tank

Before emptying the black RV waste tank on your vehicle you should be sure to put on rubberized gloves to protect yourself against any pathogens. Because it can get messy at the dump station, some people also choose to wear masks to help avoid experiencing the unpleasant smells. Prior to attaching the waste hose to and dumping your black water tank, Dave recommends making sure both valves are closed so you don’t get an unsanitary surprise when taking off the sewer dump cap. Trust us, you don’t want to skip this step!

Next, Dave shows you how to attach the (clean!) dump hose to the bayonet dump valve and empty the black water tank first, followed by the gray one. Emptying the black water and then the gray tank will help flush the hose of the black water sewage with the cleaner of the two water tanks, making it easier to perform the final cleaning with fresh water from the dump station. Additionally, this whole process can be simplified and further sanitized by affixing an extendable hose with an aftermarket funnel. This way, you can run the hose straight through your tank compartment and just drive right over the dump tank.

To make emptying an RV waste tank a breeze, there are several other aftermarket products available such as a clear dump valve connection to see when clean water is coming through the dump valves, and dump hose adapter ends to make an even more secure connection at the dump station. Invest a bit of money, and you’ll never have to worry about a messy cleanup!

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10 Responses to “RV Black Water Tank Overview”

    • Customer Service

      Dear Carroll,

      Thank your for your patience. In response to your question-
      It really depends on how it was installed. There are some manufactures that just screw the flange into a female pipe end and those can easily be removed and replaced. Most manufactures unfortunately glue them to the plumbing going into the tank. If this is the case, most of the time the whole tank has to be replaced along with the flange. There are some tanks that leave enough room to ut the piping and installed a union from the flange but you have to be quick and precise or it will leak. On upper floor units like fifth wheel bathrooms, the plumbing is a lot easier to replace. Most travel trailers and motor homes will have to have the whole tank replaced if it was glued. I would really inspect the area and see if replacing the flange is possible without replacing the whole tank. I hope this helps!

      RV Repair Club Technical Expert

    • Customer Service

      Hello Catherine,

      Yes, all plumbing systems in RV’s are not supposed to leak. They technically aren’t “closed” systems since they have open vents for air flow, but there should not be any leaks. You would have to trace the leak and find out what is causing it. Most common is a connection in the plumbing wasn’t installed properly or has become cracked. Most can be replaced but cutting off the old plumbing and installing new fittings. They do make patch kits for small holes or cracks, but those are used more on the tank itself or the piping. Not on the connections. If you are experiencing a leak, I would try to fix it and not just let it go. Especially the black tank, sewer contents are not allowed to just be coming out onto the ground.


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  1. Donl

    When we bought our air stream the service manager told us the putting 3 bags of ice down the toilet then driving around while pulling the travel trailer will often help break up any solids that may have lodged in the tank and lines. We were also told that after emptying the black water tank run clean water into the system for 5 minutes leaving the black valve open to help flush out any residue then close black tank.valve and empty gray water tank. Maybe that will help???

  2. Chuck

    I am new to Rving and recently purchased a fifth wheel. Had it a day and yes the seller knew the air conditioners were bad but “forgot” yea right to tell me. Expensive Rookie mistake. Just found out the waste tank is solid clogged. Can anyone please help me with ideas to break up clog without replacing the tank which frankly is too expensive for me right now. All your thoughts and unclogging ideas are GREATLY APPRECIATED. Thanks, Chuck aka idiot

    • jean.wozniak

      Hi Chuck, thanks for visiting the RV Repair Club site. Tires are one of the most discussed, dissected, and blogged about topics in the RV industry and you’ll find more “opinions” on RV tires than anything else. Three key components to factor into RV tires are: Proper tires, proper inflation, and proper weight. Before you slap on a set of LT tires, I would suggest visiting the experts on RV tires at: http://www.rvsafety.com They have over 30 years of experience working with tire manufacturers, RV manufacturers, and owners collecting data on weight ratings, tire failure issues, and proper tire maintenance. You will save yourself a considerable amount of money and headaches down the road by spending a few minutes on this site.

      • John

        I always put about five gallons of water and a sewer treatment tablet before travel.. this help to clean side walls and soften any residual waste left. As someone mentioned ice and treatment tablet is probably not a bad idea.

  3. Chuck Borcher

    I agree with never leaving the Black water value open as the liquid will drain leaving the solid in the tank. However, when we are camping for an extended time, I do leave the gray water value open. I have forgotten the grey water value is closed and after several showers, it has backed up into the shower. I try to anticipate dumping the black water tank and will close the grey water value the night before to accumulate some water to raise the black water from the hose after dumping the black water tank. Then after dumping the black water tank, I will open the grey water value and leave it open.

    • Rich

      I do this as well, is there any downside to leaving the grey water valve open if you’re at a campsite for an extended period? Like Chuck, I also time things to let the grey water build up before dumping the black water tank (which of course we only open when dumping).

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