|MadSci Network: Engineering|
Vodka you say? According to the freezing point depression tables in my trusty old CRC (Chemical Rubber Co.) hand book (1971 pg D-188) you'd need about a 25% solution to lower the freezing point all the way to 10F. That's about 2gal of vodka in your 7gal tank. 50 proof wash water might be interesting but perhaps a bit expensive. I don't know how often you fill your tank or the initial temperature of the water source you use, but you might get away with 1/2 to 1 inch of Styrofoam insulation wrapped all around the tank. I'm not sure of the shape of your tank but using as a sort of worst practical case something shaped like a slab-sided old jerry can, an admittedly simplified calculation using about 50F water to start shows a time to cool to freezing of at least 48 hours for an inch of Styrofoam. You might also consider heating a gallon or two of water to a nice dishwashing temperature and pouring it into the tank each night to extend this time, especially if the tank has had plenty of time to cool since its last filling. I would think another real problem might be the spigot or supply lines, if any, freezing. This could be where a really low watt heat tape and insulation of some sort would be useful. I hope this helps keep the dishes clean and the tank unfrozen.
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