Should You Empty the Grey or Black Pumping Tank First?

To keep your RV in good condition, you must regularly perform some basic maintenance tasks. One of those tasks involves emptying the black and grey tanks. But do you empty the grey or black tank first? Some people say always to empty the black tank first, while others say to empty the grey tank first. 

So should you empty the grey or black pumping tank first? This article shares everything you need to know about emptying RV holding tanks.

Understanding an RV Septic System

A recreational vehicle’s septic system usually comprises three tanks to ensure seamless operation:

  • The freshwater tank holds clean water for the RV’s sinks and shower. You only need to fill this tank when your campsite doesn’t have access to city water. If the campsite has a city water hook-up, you don’t need to fill this tank. 
  • The grey tank holds the dirty water from the kitchen sink and shower. Some vintage RVs and used campers do not have this tank. 
  • The black water tank is usually the scariest to RV travelers as it holds wastewater from the RV’s toilet. This tank holds all the dirty water for RVs without a grey water tank. 

These tanks need regular maintenance to keep the septic system working efficiently. Draining the black and grey water tanks regularly is critical. That makes knowing how to drain the black water tank and grey water tank important. 

Draining camper holding tanks proves relatively easy. But do you empty the grey or black tank first? Keep reading to find out.

When Is the Best Time To Empty Your RV Holding Tanks?

There is no fixed period after which you should empty your holding tanks. You might want to dump your tanks every other day if you travel with a large group. For only a single couple, you can go for as much as a week before emptying your RV holding tanks. 

Generally, you should wait until your tanks are two-thirds full before dumping them. This creates a smoother flow when dumping, promoting the efficiency of the process. Most RVs manufactured within the last decade have sensors that indicate how full each tank is. 

However, the design and location of the sensor vary from one RV to the next. Your RV should be on level ground for these sensors to provide accurate information. We advise checking the sensors every day to understand how long the tanks take to fill, especially if you are a beginner.

It’s worth noting that the sensors usually indicate full a little earlier before the tanks actually reach their capacity levels. You may sometimes forget to check the sensors, letting the tanks overflow. In that case, fresh water will stop draining from the taps if the grey tank becomes full. 

You will experience the same phenomenon when the black tank fills up, but the experience will be nastier. To avoid horrible experiences, you should dump your holding tanks as soon as the sensors indicate “full.”

Related: Septic Tank Never Needs Emptying

Do You Empty the Grey or Black Tank First?

Many RV travelers empty and flush the black and grey water tanks at the same time. The black and grey water tanks use the same relief hose to drain into the dump station’s disposal tank. So, you should follow the best practice and empty the black tank first.

Then you can use the cleaner grey water to flush any traces of black water out of the relief hose. 

After dumping both tanks, flush them out thoroughly. Besides knowing which tank to empty first, it is important to know how to empty camper tanks properly to ensure the best results. 

How To Empty Holding Tank on RV

Follow the steps below to dump your black and grey RV holding tanks safely and efficiently:

  • Put on safety gloves: You need to protect your skin against any harmful incidents while handling the hoses containing waste and contaminated water. 
  • Hook the relief hose up: Connect your relief hose to the RV drain and the dump station. Ensure you use an elbow connector to prevent wastewater spillage while dumping. 
  • Drain the black water tank: Pull the black tank’s valve, allowing it to run until you no longer hear the sound of water flowing. Close the tank once done. 
  • Empty the grey water tank: Pull the grey tank’s valve, allowing it to run until you no longer hear the sound of water flowing. Close the tank. 
  • Fill the black tank: Hook a garden hose from a water source to your RV’s black tank valve. Allow the water to run until the tank fills, and then turn the water off. Consider using a separate hose from your fresh water to avoid contamination. 
  • Empty the black water tank: Pull the black tank’s valve to allow the water to drain out. 
  • Repeat the process: Fill the black tank with clean water and empty it once or twice until the water is clear. 
  • Treat your holding tanks: Put a holding tank treatment tab in your RV toilet bowl and flush it with a full bowl. 

Can You Drain a Grey Water Tank Without Connecting to a Dump Station?

Now that you know how to empty grey water tank on RV, you may also want to know if it is possible to drain your grey tank without hooking it to a dump station. Some municipalities require you to empty grey water from the RV tank into an official dump station. 

In other municipalities, you may use grey water for other purposes, such as lawn watering. However, it is critical to consider the content of your grey water tank before using it for other things. 

Food particles and grease from washing plates can cause a mess on your lawn. Additionally, the smell can be unbearable if the grey water has been in the tank for at least a week. You should also realize that non-organic soaps can interfere with soil chemistry and negatively impact vegetation growth on your lawn. 

Therefore, if you do not know the exact contents of your grey water tank, it is best only to dump it at an official dump station. The dumping fee is usually affordable. Some municipalities will allow you to empty your grey water tank directly into their established sewer system. 

Preventing RV Holding Tanks From Clogging

Your grey and black water tanks can clog over time without proper care and maintenance. The clogging will make your RV septic system less efficient. You can prevent this problem by ensuring that water alone flows into your grey tank. 

Your shower and kitchen sinks should have drain covers to catch solid particles. You should also wipe all dishes with a rag before washing them in the RV sink. The only things that should go into the toilet are septic-safe toilet paper and human waste. 

You can even find special RV toilet paper in many local stores. But how can you unclog your black tank if it gets clogged?

A simple and quick solution includes using a reverse RV flush valve. This valve will force water into the RV plumbing lines to break the clogs. Simply hook the valve to your RV drain and connect it to a garden hose. 

When you open the water, the valve will push the water into the RV pipes and tanks to remove any obstacles causing your tanks not to empty efficiently. 

should you empty the grey or black water pumping tank first

Tips for Maintaining RV Holding Tanks

Knowing how to empty camper holding tanks is not enough. You should also learn some best practices to keep the tanks clean and functioning efficiently. Below we list a few tips to get you started:

Use Appropriate Toilet Paper

Using the right toilet paper is one of the simplest ways to keep your RV black tank in good shape. You should use only single-ply toilet paper that quickly dissolves in water. 

Flush Holding Tanks Regularly 

Regular flushing plays an integral role in RV holding tank maintenance. Whenever you dump your black holding tank, ensure you also flush it. Fill the tank with clean water and dump again until you see clear water coming from the tank. 

Treat Your Holding Tanks

Once you empty your grey and black water tanks, use a holding tank treatment. These treatments help break down toilet paper and waste to prevent clogging. The treatment tabs are usually scented to help neutralize foul odors in your recreational vehicle. 

Keep the Valves Lubricated

You should always lubricate the handles of your RV holding tanks. Without proper lubrication, the handles can stick, causing your tanks to stick in the open position. Regular lubrication helps prevent sticky handles. 

To lubricate the handles, start by emptying the holding tanks. You already know how to drain the black and grey water tanks. Next, pull out one handle before spraying Teflon lubricant on the metal rod. 

Once you lubricate the handle, pull it slowly in and out several times. Follow the procedure for the other holding tanks. Avoid twisting the handles when pulling them out to prevent damage to the connecting cables. 

Keep the Fresh Water Tank Sanitized

Sanitizing the RV fresh water tank is critical to maintaining the RV’s septic system. You should sanitize your tank with bleach after contamination or storage. 

Final Thoughts

Do you empty the grey or black tank first? You can empty both holding tanks at the same time. However, starting with the black tank works best, so you can use the much cleaner grey water to flush the relief hose. 

If you need professional help to empty your RV holding tanks, Wilkinson Portables can help. The company serves California’s El Dorado County, including Placerville, Plymouth, and the Greater Sacramento area, and can pump from RVs of all sizes. 

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