Most RVs have two types of holding tanks on board: a gray water tank and a black water tank

A gray water tank collects water that goes down the drain of your shower and sinks. The black water tank holds the wastewater from your toilet.

Though it may seem easy to do, you can't just empty your tanks and be on your merry way. Buildup in the black water tank will cause unpleasant odors and potentially disastrous blockages. A clean tank also helps the tank sensors work better, giving you the most accurate readings possible when it comes to the contents and fullness of your tank.

A dump station is ideal for dumping your gray water tank, but dumping a black water tank at a dump station is problematic for two reasons:

• You can't always assume that a dump station will have a hose connection
• The process, if done properly, can be more time-consuming

Cleaning your black water holding tank is best done when you're fully hooked up and have both a water and sewer connection.

Avoid using bleach or antifreeze for your deep clean, as both of these can dry out rubber seals and ultimately ruin your sewage system. Simple Green All-Purpose Cleaner doesn't contain the harsh chemicals commonly found in other cleaning products. It also deodorizes, so you can remove stubborn soils and debris while leaving your RV bathroom smelling fresh at the same time.

Emptying and cleaning will vary based on how often your RV bathroom is being used, and how many people are using it. At the very least, you should do a deep clean after each trip, as you won't want to store your RV with wastewater in the tanks. Otherwise, it's recommended that you clean your RV tanks monthly in the summer and every other month in the winter.

Directions for Cleaning an RV Black Water Tank:

Before you begin, you'll need a length of a garden hose that you will always use specifically for cleaning the black water tank. You'll also want to have a backflow preventer on your hose to keep water from coming back into the freshwater system from the black water tank flush. It's recommended that you dump when your tank is ¾ full.

Be sure to protect yourself from any drips, leaks, or splatters by wearing gloves.

1. Close the gray water tank valve the night before cleaning. Usually, this can stay open when you're hooked up, but you'll want to accumulate some water to rinse the sewer line after you've dumped your black water tank. Leave the gray water tank valve closed overnight so you can gather about half a tank of water.
2. Clean your toilet. Click here for directions on how to do this with Simple Green All-Purpose Cleaner. Make sure you turn your bathroom fan off before you start this process (it should also be off every time you flush your toilet). Don't forget to open the gate valve and use a brush to scrub the area. Harsh cleaning chemicals can damage the seal in the hole of the toilet that keeps odors from coming up from the black water tank. After you've scrubbed, flush your toilet several times.
3. Connect your hose. Connect the anti-backflush valve to the end of your garden hose. Attach the hose to the sewage rinse attachment on the RV, and the other end to your fresh water source.
4. Slowly turn on the water. Don't turn it all the way on at first.
5. Pull the black water tank valve.
6. Slowly turn the water on more. Run it until the exiting water is mostly clear.
7. Close the black water tank valve. Leave it closed for about a minute.
8. Open black water tank valve again. Let the water continue to run through.
9. Close black water tank valve again. Leave it closed until the tank fills up. Watch closely as the tank fills up - don't leave it unattended, as you don't want the tank to overflow and pour water out of the vent on top of the RV.
10. Open the black water tank valve as soon as the tank is full. The water should run mostly clear. If it's not clear, fill the tank again and repeat steps 7 through 9.
11. Turn off your water. Let the remaining water drain out of the tank, then close the valve.
12. Open the gray water tank valve again. Let that water drain.
13. Head back inside the RV to the bathroom. Pour 2 ounces of Simple Green All-Purpose Cleaner down the toilet followed by a gallon of water.
14. Perform a smell test.
1. Close all of the windows in your RV, open your toilet's gate valve and turn on your bathroom fan. There should be no odor coming from the black water tank.
2. If you smell a lingering odor, pour 2 more ounces of Simple Green and one more gallon of water down your toilet.
3. You can also put ice in your toilet. You'll pour about five 10-pound bags of ice down the toilet. Then you'll need to go for a drive as the ice melts. As it melts and shifts around the bottom of the tank, it will scrape up any debris stuck on the bottom. Then you'll dump the tank one more time to drain the melted ice and any debris that was scraped up.
4. As your last line of defense for really smelly tanks, you can pour one cup of Simple Green and one gallon of hot water down your toilet, then slowly fill the tank with water. Let the solution sit in the tank for 24 hours. Drain it, and do the smell test again.

If your RV does not have a sewage rinse outlet, use these directions:

Before you begin, you'll need a length of a garden hose that you will always use specifically for cleaning the black tank. It's recommended that you dump when your tank is ¾ full.

Be sure to protect yourself from any drips, leaks, or splatters by wearing gloves.

1. Close the gray water tank valve the night before cleaning. Usually, this can stay open when you're hooked up, but you'll want to accumulate some water to rinse the sewer line after you've dumped your black tank. Leave the gray water tank valve closed overnight so you can gather about half a tank of water.
2. Clean your toilet. Make sure you turn your bathroom fan off before you start this process (it should also be off every time you flush your toilet). Don't forget to open the gate valve and use a brush to scrub the area. Harsh cleaning chemicals can damage the seal in the hole of the toilet that keeps odors from coming up from the black water tank. After you've scrubbed, flush your toilet several times.
3. Connect your hose. Connect your hose to your freshwater source. Feed the other end down the hole of your toilet.
4. Turn on the water. Turn the hose on the highest it can go - you want to hear it flopping around inside the tank. This ensures the water is reaching the spots that the built-in sprayer can't get to.
5. Pull the black water tank valve. Let the water run for 10-15 minutes, but don't leave it unattended.
6. Close the black water tank valve. Leave it closed for about a minute.
7. Open the black water tank valve again. Let the water continue to run through.
8. Close the black water tank valve again. Leave it closed until the tank fills up. Watch closely as the tank fills up - don't leave it unattended, as you don't want the tank to overflow and pour water out of the vent on top of the RV.
9. Open the black water tank valve as soon as the tank is full. The water should run mostly clear. If it's not clear, fill the tank again and repeat steps 6 through 8.
10. Turn off your water. Let the remaining water drain out of the tank, then close the valve.
11. Open the gray water tank valve again. Let that water drain.
12. Head back inside the RV to the bathroom. Pour 2 ounces of Simple Green All-Purpose Cleaner down the toilet followed by a gallon of water.
13. Perform your smell test as the above directions state.

TIP: Never leave your black water tank valve open, even when you're fully hooked up. This will lead to what is known as "pyramiding," which is when all the liquid runs out of the tank, leaving the solids to build up and harden.