[JRTJH]

Depending on the fresh water tank location and whether there might be some "residual water" that won't drain, you might find that any antifreeze you put into the tank is diluted to a "non protective solution". What I mean is that most FW tanks are "long, wide, short" tanks. If the trailer is slightly off level and the drain end is "at the high point" you could have 3 or 4 gallons of water that won't drain out of the tank. If your antifreeze (on the label) says it protects to -50F (at full strength) and only to +20 at 50/50 dilution, and you pour in 5 gallons of antifreeze, run it through the plumbing, you may only have a solution that will protect against freeze damage to 15 or 20 degrees....

So, check to make sure that there's no left over water in the FW tank before you start "adding and mixing" antifreeze to the tank. You may not have the protective value of the antifreeze that you think you have.....