Hi Bbycakes,

A black discharge could indicate an ear infection or mites. Mites, however, are not common in adult dogs. You can read about them here:
http://www.marvistavet.com/html/body_ear_mites.html

It is probably a yeast or bacterial infection. You can use a mixture of distilled vinegar, water and alcohol on a cotton ball to gently clean the ear

In a yeast infection, you will see a golden to black buildup in the ear. You may also notice redness and bleeding, head shaking and your dog scratching the ear as well. You can try some miconazole cream to see if it helps until you can get in to see the Vet, but it isn’t a cure for underlying condition. A bacterial infection might not have much of an odor.

You will have to have your vet look at it and determine if it is mites, fungal or bacterial in nature so the appropriate medication can be given. Ear infections are not pleasant for your dog and I hope you can get him seen soon.

The following site has a recipe for a home remedy that may provide some relief though I recommend visiting the vet for medication.
http://www.woodhavenlabs.com/ears.html

Zymox with cortisone has been used by some experts to clear ear infections as well. You can read about it here:
http://animalpetdoctor.homestead.com/Zymox.html

I hope this information is helpful to you.