Trailer is in storage, and last night the temps dipped into the high 20's F. I happened to go check on it and saw that the antifreeze in the toilet had turned to slush and was almost frozen. I didn't think that was normal so I contacted the mfg, FVP. Below is their (long) response. Apparently it's supposed to freeze. Who knew:
"It is a common misconception that because our RV & Marine Antifreeze freezes, it’s not providing the burst protection that is claimed on the label. That being said, the product could be also called “Anti-Burst”, because it is the burst protection that you are buying, not the antifreeze property that the label name suggests.
In fact, the burst protection is unrelated to the freeze point. Just because the product is frozen does not mean that there is faulty burst protection. Depending on the formula you have, the product will freeze in the 16-20oF range, and this is completely normal and expected.
Rest assured, we do extensive, third-party burst testing (so as to remove any bias) and our results always exceed our label claim.
Hey! You’re not alone here! We get this question a lot and rest assured this is completely normal.
The product is designed to become solid at lower temps so it can do its job which is protecting your beloved pipes from bursting! The key with RV/Marine Antifreeze is BURST protection.
To go a little technical – the product can start to appear solid at +16F to +20F. So yes it will go solid but it is protecting your pipes.
Please feel free to provide your contact information and we can reach out if you have additional questions.
RV/Marine antifreeze is rated by burst protection, an industry standard term to define the strength of protection at very low temperatures. Historically this product class has been called antifreeze though it is designed for burst protection NOT freeze protection. Current formulations of common RV/Marine antifreeze can form slush or become frozen at temperatures near +20F. This is completely normal and does NOT affect the protection at the advertised burst protection temperature. Frozen RV/Marine antifreeze does not mean the product is defective, it simply means some of the water solution in the product has begun to crystallize but not expand to a maximum solid state."