What Happens When Grey Water Tank Is Full? A Detailed Answer

What happens when grey water tank is full?” is a prominent question among new RV owners who are worried about their waste water compartment. In the best-case scenario, a deep shower pan prevents overflow damage. But in other situations, you risk a ruined carpet, unpleasant odors, and potential floor damage if you don’t address it promptly.

What Happens When Grey Water Tank Is Full ~ Ran When Parked

For further insights on overflowing gray tanks, keep reading this article to be well-prepared when you encounter this issue.

What Happens When Grey Water Tank Is Full?

When the grey water tank is full, there is a high likelihood that your RV carpet will get ruined. If it becomes too full, floor damage may be inevitable, which often comes with foul odors. You risk more extensive damage if you do not promptly address the issue.

In most RV designs, grey water tends to back up into the shower because the RV shower is typically the lowest point in the vehicle. When this happens, emptying the grey water tank promptly is crucial.

Grey water overflow isn’t as messy as black water tank issues but can still create problems. Wet carpets, cabinet bottoms, flooring, and potential spills can occur in the main RV area.

Catching the grey water tank overflow quickly minimizes damage, primarily dealing with the odor. Prolonged exposure to water can cause mildew, resulting in persistent odors and potential carpet replacement. Addressing cabinet damage may also become costly if the water damage is severe.

How Can You Know When Your Grey Water Tank Is Full?

You can know when your grey water tank is full by checking the sensor. Most modern RVs are equipped with sensors on their grey water and black water tanks to monitor tank levels. When the water reaches the full mark, a control panel light signals that the tank is full.

Alternatively, you can check your shower or sinks for standing water. If you find water in the bottom, it’s an indicator that your tank requires emptying. Also, if the sink drain is slow or clogged, it suggests a full gray water tank.

However, sensors can be inaccurate and malfunction. To accurately determine the true full line, an old-school trick is to pour 5 gallons of water down the shower drain until you see water at the bottom of the shower pan.

This method reliably identifies the actual full level. Nevertheless, when the sensor light appears, it’s a prudent practice to empty the tank to be on the safe side.

How Can You Know When Your Grey Water Tank Is Almost Full?

You can know when your grey water tank is almost full by paying attention to the tank gauge and signals. You can even simply inspect the gray water tank periodically to notice overflowing. Sometimes, an unpleasant odor within your RV will tell you that your gray tank is almost full.

You can use various methods to check if your black and gray water tanks are full. Employing multiple methods is wise if you’re uncertain about the tank levels. Being cautious is essential, as letting the waste levels rise without knowing how full they are can be risky.

Check the Gauge

Many RV owners initially rely on the tank gauge to assess their waste water tank levels. This monitoring system reads tank fullness and signals when it’s time to empty the tank at a campground.

Checking the Gauge ~ Ran When Parked

However, sensors can occasionally provide inaccurate readings, especially if debris or tissue accumulates on them, resulting in a false full reading. Therefore, having alternative methods for checking waste water tank levels is beneficial.

Examine the Grey Tank

You can determine the water level in your RV gray waste tanks by inspecting the underside of the camper. If the tank is made of translucent plastic, you can use a flashlight to gauge the liquid level. This method is handy for assessing your freshwater supply if other measurement tools, like the freshwater gauge, are malfunctioning or unreliable.

Check That the Shower Drain Holds Water

When the grey water tank fills up, the water will head to the lowest drain point. This is usually the shower drain. If you notice the floor of the shower starting to hold water, it could be because the levels in the grey waste tank are too full.

Checking That the Shower Drain Holds Water ~ Ran When Parked

It’s best to drain the grey and black water in an appropriate place as soon as possible to avoid any spills or unpleasant leakage.

Don’t Ignore Odors

When your RV toilet starts emitting unpleasant odors, it’s a sign that your tank may require emptying or at least a check to assess its fullness. Your sense of smell effectively indicates when the black tank needs attention. So, if the odor is worsening, it’s time to head to the dump station.

What Should You Do When Your Grey Water Tank Becomes Full?

When your grey water tank becomes full, you should dispose of the waste. You should wait until the tanks are reasonably filled because increased liquid levels can aid in flushing out solid waste when you empty the tanks. It is also ideal to dispose of the waste at authorized dumpsites.

Emptying the black tank when it’s not sufficiently full may lead to solid waste becoming stuck and necessitating a thorough flush to clear it. A practical approach is to wait until the tanks are about ⅔ full before emptying.

Start by opening the black tank valve, followed by the gray water valve to allow the water to backflow into the black tank, aiding in residue removal.

Where Should You Drain Your RV Gray Water Tank?

You should drain your RV gray water tank at authorized RV dumpsites. Specific dumping areas are designated for it. Illegal dumping, often called stealth dumping, can result in fines in most places. However, if reaching one is a concern, you may empty the tank in a remote, green area.

Dumping laws vary by state and location, so always check the rules and restrictions of where you plan to dispose of your waste. In most areas, direct greywater dumping on the ground is prohibited. However, some places encourage it for irrigation purposes. Here are key points to remember:

  • Avoid dumping grey water on pavements, as it can produce unpleasant odors, especially if it contains food waste.
  • Never contaminate freshwater sources, such as lakes, with your sink water.
  • Always verify the rules and restrictions of your chosen dumping location and be considerate of others in the area.

Whenever you’re at a campground with dumping facilities, it’s best to use them. Even seemingly small discharges can collectively create a messy campground if all RVers empty their grey water tanks on the grounds regularly.

How Can You Effectively Drain Your Grey Water Tank?

You can effectively drain your grey water tank by simply attaching a sewer hose to the designated RV dump station hole and connecting the other end to your grey water tank valve. Then, open the tank’s valve and allow the waste to drain.

Here are essential steps to keep in mind when draining your gray tank:

Insert the Drain Hose in the Dumping Station Drain

Open the lid of the dumping station’s drain. Extend your RV’s drain hose and insert the lower end into the drain. Ensure that approximately 4 to 5 inches of the hose is inside to prevent wastewater splashing.

Inserting Drain Hose in the Dumping Station Drain ~ Ran When Parked

Gently tilt the drain’s lid forward, allowing it to rest on your drain hose to secure it in place during the tank emptying process.

Attach the Other End of the Hose to the Grey Water Outflow Valve

Start by taking off the cap from your RV gray water outflow valve. Then, connect the upper end of your drain hose to the outflow valve. Use a sewer hose support system to prevent kinks or dips that can hinder wastewater flow.

This system comprises a series of interconnected C-shaped plastic props that unfold like an accordion. The drain hose rests loosely in the semicircular parts of these props.

Open the Outflow Valve and Let the Tank Drain

With the upper end of the drain hose firmly attached to your RV’s grey water outflow valve, go ahead and open the valve. This will permit the wastewater from your tank to flow through the hose into the drain at the dumping station.

Opening Outflow Valve and Letting the Tank Drain ~ Ran When Parked

Close the Valve and Remove the Hose

After the grey water tank has completely emptied, shut the outflow valve. Then, disconnect your drain hose from the outflow valve, as the hose may still contain a small amount of water you don’t want dripping onto your skin or clothing. Put the cap back on the outflow valve.

Rinse Your Drain Hose

Utilize the non-potable water hose at the dumping station to rinse your drain hose. Let the water flow through the drain hose and into the station’s drain. Afterward, return the non-potable water hose to its designated location.

Rinse Your Drain Hose ~ Ran When Parked

Detach the Drain Hose and Use a Tank Treatment

Lift the drain lid at the dumping station to free your drain hose. Carefully detach the RV drain hose from the station’s drain, then replace the drain’s lid. Use sanitizing wipes to thoroughly clean the exterior of your drain hose, with extra focus on the ends. Coil up your drain hose and store it properly.

After you’ve emptied the gray tank and securely closed its outflow valve, proceed to pour the appropriate quantity of grey water treatment down the shower pan drain.


Regularly emptying the tank is crucial to maintain the condition of your RV and ensure cleanliness. Let’s examine the important points discussed in this article:

  • A full grey water tank can lead to RV carpet damage. It may result in floor damage and foul odors if you leave it unchecked.
  • Check the built-in sensor to determine if your gray water tank is full. When the water reaches the full mark, a control panel light indicates the tank is full.
  • Dispose of the waste from your gray water tank once it reaches full capacity. It’s best to use authorized dumpsites for proper disposal.
  • Efficiently drain your grey water tank by connecting a sewer hose from the designated dump station hole to your grey water tank valve. Open the tank’s valve and let the waste drain out.

A full grey tank can lead to plumbing issues and unpleasant odors. Always remember to empty the grey water tank into the appropriate dump stations or portable holding tanks when it reaches capacity.

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