Angelbow: I have two cats who regularly get ear infections. Er, I should say USED to get.

My vet has giving me an ear wash, good for dogs, cats, puppies and kittens. As long as I use that twice per week, we are free of infections. The vet said once per week should be enough. I decided to do twice per week; that way, if I miss one day, I don't need to worry just stay on my schedule.

It isn't very expensive at all, you can order it on line as it does not require a prescription. Preventing the infection in the first place has been most helpful for me.

Two different products, do the same thing. One ear wash is Oti Clens. The other is MalAcetic Otic.
Same routine with each wash. Put in a few drops, use a cotton swab to clean out the ear. And remember to wear your rain gear so you don't get soaked with the inevitable head shake.