a. Vodka clean the tank by dissolving aluminum. It is actually far more corrosive than glycol or water. I did the side-by-side testing using standard methodology.
b. After the vodka ferments (which can happen to any under strength AF glycol or alcohol), it will be nastier than the half-empty bottle of Boones Farm under your back seat. This is the nasty taste people observe in their systems, not a "chemical" taste. Vodka is ONLY antiseptic if maintained about 25% ethanol. You won't need a few bottles, you will need 50/50 vodka/water, which will cost 2-3 times more than AF, even if you shop the bottom shelf.
c. Alcohol is rough on some of the plastics and elastomers. I would not put it in my boat in any form (other than the liquor cabinet).
d. Without dye, it will be hard to tell when the vodka is coming out the other end.
The Vodka thing is a tired myth. It makes no sense on any level (corrosion, cost, taste). Can't we bury it?