Vodka will not sterilize: Ster. alcohol, isopropanol or ethanol, work only if 70% with remainder as water. Worse, the dissolved alcohol evaporates over time. Got my arse chewed out on the job about this.
You can do several things all at once: water in airlock, attached to a wetted cotton-filled filter tube, attached to a length of tubing. Pasteur showed, 160 years ago, that live stuff could not get up the tube to infect a nutrient solution. All cheap, dependable safeguards.