The treatment Vet's use for yeast is usually Zymox - I think thats the one you might be thinking of, Wylie's Mom! A lot of dogs have yeasty ears - My Cavalier, Louis, is like a permanent yeast factory b/c its worse in floppy eared dogs & warm climates.
I have to clean his ears 2X a day with an herbal flush!
I use Halo Herbal ear wash and its good to get in the habit of cleaning your pups ears a few times a week, or more if he is prone to getting yeasty. Regular cleaning ensures you catch yeast right away and are familiar with your dog's ear anatomy in case anything changes, you'll notice it immediately.
Zymox is an antifungal, not an antibiotic, so its very safe and it does wonders. It is messy, esp. for our little ones. Ella Bean hates having her ears cleaned, but Louis loves it, esp. the massage part.
A good way to make it more pleasant is the use a nasal aspirator like you use for babies and dilute some of the ear wash in warm water. The main reason dogs don't enjoy ear cleanings is that the liquid is much colder then their internal temperature, so its like shooting ice water in their ears! You can't dilute the Zymox, but you can teach your dog to enjoy ear cleanings!
You can also add probiotics in to theit diet which helps keep yeast at bay among plenty of other benefits!