Fifth wheel RVs have onboard black and grey water holding tanks that need to be
emptied on a regular basis. The black water tank holds the waste from the toilet
and the grey tank holds water from the sinks in the 5th wheel. There are normally
three holding tanks on a 5th wheel RV. Sometimes new owners do not realize that
there is a grey water tank close to where the kitchen is in the RV, so that tank
does not get emptied causing the kitchen sinks to backup. To empty the kitchen sinks
grey tank, there is a handle that needs to be pulled to dump the water down to where
the main grey tank is toward the back of the 5th wheel.
It is recommended you wear gloves for dumping your tanks.
First you will need to connect the sewer drain hose to your Fifth Wheel sewer drain and the other end
of the hose that has the 90 degree elbow to the sewer drain.
The black water tank should always be dumped first, and then the grey water tank. This ensures that
the grey water washes out the hose of all back water debris.
Your black water tank should only be dumped after it approx. 35 percent full or more. This makes sure
that there is a good flow of water to help wash everything down the sewer drain.
To dump the tanks you need to open the black tank gate valve which is located in
the sewer compartment on your RV. This is a T-handle that is normally attached to
where the discharge pipe is much larger in diameter. Some 5th wheels might have
an electronic discharge switch that will automatically open the valve when you press
the switch. These automatic valve openers can easily be installed if you want the
ease of not having to mess with the T-handle which can be difficult to open at times.
After the black water has finished dumping close the valve and then open the grey
water tank valve and dump that water, which will clean out the sewer hose.
Remember to dump the kitchen grey water tank which will be located in a storage compartment close to the kitchen.
Sometimes the kitchen grey tanks T-handle can be a little diffcult to find and get access to.
If your 5th wheel black tank has a flush adapter you can connect a hose from a faucet and rinse out the
black tank to ensure that it stays clean. If the black tank is not maintained properly,
the tank gauge will stop registering correctly at some point as it will have debris
If you don’t have a flush adapter on your tank you can use the Flush King adapter to rinse the black
Once both holding tanks are dumped, elevate the sewer hose to make sure all the water runs into the
Disconnect the sewer hose and replace the sewer cap on the 5th wheel sewer pipe.
RV Site With Sewer Connection
If you are in a RV site and hooked up the sewer you still need to keep both the grey and black water
tanks closed. If you leave the black water tank open while you are connected to
the sewer, all of the water will drain from the black tank and only tissue paper
and solids will be left which will dry out and become a problem to clean. You will
also get the smell from the sewer coming up into the bathroom of the RV. You will
need water from the grey tanks to clean out the hose every time you dump the tanks.
Fifth Wheel Black Tank Maintenance
Make sure you regularly flush the black water tank with clean water to get out as much debris as possible.
This will help eliminate odors in the Fifth Wheel.
How To Dump Your Black Tank With No Sewer Connection
If you are staying in a RV Park that does not have a sewer hookup, but has a dump station then you will need
a portable holding tank that you can transport to the dump station. You dump the waste from your RV into this
portable tank and then hook it to the back of the truck and take it to the dump station.
The key with portable holding tanks is that they need to be rugged and preferably have large wheels.
Most parks that do not have dump stations tend to have gravel or dirt roads and the heavy holding tank
takes a beating every time it is dragged to the dump station. A 40 gallon portable holding tank when full will weight approx.
320 lbs. You also need to be aware how much the
portable holding tank can hold and plan accordingly before you dump a full 5th wheel black tank into it.
Rhino Portable Holding Tank
Below is a very informative video showing how to dump your tanks, how to clean the tanks and the use of
ice for black tanks that have not been cleaned in a while and need a thorough cleaning.