Winterize a travel trailer by removing and bypassing any in-line water filters, draining all holding tanks and lines, draining and bypassing the water heater and filling the plumbing system with the appropriate antifreeze. Consult the appliance owner's manual for procedures involving third-party icemakers and washing machines.
Bypass any in-line water filters so they aren't fouled with antifreeze. Drain the fresh, grey and black water holding tanks. Flush the grey and black water tanks either automatically, if your trailer is equipped to do so, or with an appropriate cleaning solution. Lubricate the termination valves with WD-40.
Open all of the hot and cold faucets, toilet valves and outside shower fixtures. Drain the water heater, but make sure it is cool and all of the pressure has been released. Locate and open the low point drain lines for both hot and cold water, and use the water pump just long enough to clear the lines. Recap all of the drains, and close the faucets.
Install the proper water heater bypass kit. Connect a clear hose to the inlet side of the water pump, and put the other end into a 1-gallon container of non-toxic antifreeze. Pump antifreeze into the system, replacing the container as needed, until it flows from all of the faucets and fixtures when opened and the toilet when flushed. Pour a cupful of antifreeze down each drain, close all faucets and fixtures, and make sure the water heater is turned off.