Chris Dougherty, Certified RV Technician, posted this tip while he was serving as RVtravel.com’s technical editor.
Some people prefer not to use the plumbing system during the winter for fear of doing something wrong and risking a freeze-up, and subsequent damage. Others prefer to just use the toilet, and depend on campgrounds for their other needs. It’s possible to use your RV toilet for brief periods in freezing weather.
Purchasing a four-season RV or modifying one to handle sub-freezing weather is one possibility. I have done this previously with good success. This requires a coach with completely enclosed and heated holding tanks.
I prefer to add individual tank heaters and a separate heater for the utility compartment. I have also added digital freeze alarms to those areas to make sure that the temperature doesn’t dip too low in vulnerable areas. Work off the holding tanks only, and dump when necessary. Don’t stay connected to outside utilities.
But what if your RV isn’t winter-capable? Here’s the no-water option: It may be possible to use the RV toilet without the use of water, but extreme care must be taken to prevent freezing and damage. The process involves using potable RV antifreeze instead of water to flush the toilet. Starting with a completely empty black water tank, add at least 3-4 gallons of RV antifreeze to the black tank, and continue to use the RV antifreeze to flush the toilet as necessary. When you’re done using the system, dump as usual, then there should be no freezing problem.
For you snowbirds out there, using the coach’s water system from the cold temperatures to the warm and vice-versa is an option, but I wouldn’t recommend doing so unless you’re certain that your enclosed tanks are protected well enough for the climate. An option is to use the system as pointed out above, keeping the heat in the coach on, using minimal water, and making sure there’s adequate antifreeze in the holding tanks. Many folks will start using the system in the Mid-Atlantic region, for instance, headed south, and will re-winterize there on the way back.
Whichever you decide to do, make certain that the toilet is well winterized when you are done. Small amounts of water can remain in the flush valve on some toilet models, which can freeze and crack the valve if not completely removed or replaced with antifreeze.