How to Winterize a Restroom Trailer

Guide to Proper Winterization of Lang Specialty Trailers

Steps For Effective Winterization

If you are using your trailer in below-freezing temperatures the heat and tank heaters must be kept running to keep your water lines or waste tank from freezing.

If you are storing your restroom trailer in below-freezing temperatures you will need to winterize the unit using RV antifreeze. Below are some recommended steps and procedures that will properly winterize your restroom trailer and help avoid damage from frozen pipes, broken valves, and cracked tanks. While there are many different ways to properly winterize your restroom trailer, any method that removes all water from the trailer’s waterlines, pumps, traps, tanks, and features is acceptable.

As part of our maintenance resources, we have outlined two suitable methods for winterizing your restroom trailer based on the inclusion of a freshwater system. If you do not understand the instructions or have specific winterization questions not covered here, please reach out to us at any time and we would be happy to assist you!

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Winterizing Restroom Trailers With Fresh Water Systems

Follow the below steps to properly winterize a restroom trailer with a freshwater system and protect against damage caused by the expansion of any water left over in the pipes, toilets, urinals, and sinks.

  1. Drain all water from the freshwater holding tank.
  2. Run each toilet and sink until freshwater no longer flows into the tank or from the tap.
  3. Turn off the water pump switch.
  4. Open all available valves to thoroughly drain the remaining water from the water lines (1,2,3,4,5, and 6).
  5. As an added benefit of the design of Lang Specialty Trailers, we have installed a winterization port onto the pump inlet. (Valve #5)
    1. Close valves 1, 2, 3, 4, 5, and 6.
    2. Place the winterization hose into a one-gallon jug of RV Antifreeze.
    3. Open Valve #5.
    4. Turn on the water pump switch that was previously turned off at Step 3.
    5. Open Valve #3 until you can see the RV Antifreeze moving into the freshwater tank.
    6. Open Valve #4 for ten seconds to purge all remaining water from the spray bar clean-out port.
    7. Run each toilet and sink until RV Antifreeze appears in the tank or at the tap.
    8. Dump ¼ gallon of RV Antifreeze into each individual urinal trap.
    9. Dump ¼ gallon of RV Antifreeze into each sink to fill the “s” traps located underneath each drain.
    10. If the specific design of your restroom trailer includes exterior hand washing stations make sure to induce RV Antifreeze to the sinks, water lines, and drains of these units. A minimum of ¾ gallons of RV Antifreeze is required to adequately fill the bilge pump. *A drain valve has also been installed under the trailer to drain the water from the water lines if desired.
  6. Review the restroom trailer features and functions to verify that all remaining water has been successfully purged from the tank.
  7. At this point, you can now drain the waste holding tank.
  8. After draining is complete, it is acceptable to leave the dump valve open when not in use to avoid potential freezing in the valve.
  9. Finally, raise the tongue jack high enough so that any water possibly remaining in the waste tank after this procedure does not enter the dump valve. The valve can crack due to the expansion of frozen water and necessitate additional repairs before the next use.

Trailers Without Fresh Water Systems

Any trailers without freshwater systems stored in below-freezing conditions should also undergo comprehensive winterization procedures to avoid possible damage from expanding frozen water. Thankfully, this process is quite simple and will help to avoid any unexpected or costly repairs necessary before the next use.

  1. Due to the procedures and steps required, the following winterization recommendations are best completed by two people.
  2. To start, connect an RV Antifreeze hand pump device to the city water fill inlet located on the exterior of the restroom trailer.
  3. Have one person hold down the flush valve on each toilet while the second person pumps RV Antifreeze into the trailer water line with the aid of a hand pump. Flush each toilet and run each sink until only antifreeze emerges.
  4. Open Valve #4 “Spray Bar Clean Out”, if applicable, to ensure that all remaining water is pushed out of the spray bar and into the waste tank.
  5. At this point, we recommend dumping up to a ¼ gallon of RV Antifreeze into each urinal trap and a suitable amount into sinks to fill the “s” traps located underneath each drain.
  6. You can now raise the front of the trailer higher than the back to move any remaining water in the Waste Holding Tank or additional water that may enter through the vent stack away from the Waste Dump Valve. Water left in the Waste Dump Valve that is exposed to below-freezing temperatures will expand and can rupture the valve.

Additional Trailer Maintenance Resources


Lang Specialty Trailers goal is to create innovative restroom trailers that are not only eye appealing, but are durable, easy to install, easy to clean, and functional for the professional restroom trailer operator.