How can I safely clean my dog's ears?

My black lab/chow mix, BlackJack, is 14 years old and has had dermititis all his life. As a result, he often gets a lot of build-up in his ears, and will shake his head or scratch at them to try to clear them out. The vet had prescribed a solution, but it ended up worsening his condition. I need something to put on the cotton (beyond water) to clean his ears.