Fill a sink with hot, soapy water. Use an antibacterial soap. Do not use lukewarm or cool water. It's important to make the water as hot as you can stand it for the best cleaning power.
Scrub the outside of the bottle with a sponge to remove any film. Fill the bottle about halfway full with the hot, soapy water, and use a bottle brush to cleanse the inside -- being sure to get the edges and under the lip where the nipple goes on.
Rinse the bottle in a solution of half water and half vinegar. Vinegar is effective at breaking down minerals, especially calcium and magnesium, which are present in hard water and can build up on dishes, including bottles.
Rinse the bottles off, and leave them to dry upside down.