You have replied to a post from 2011 - in case the original contributor does not see your comment I will offer some advice.
There are many uses for Geranium essential oil, and use for respiratory problems is just one of them.
You can use 5 drops of Geranium essential oil in a vaporizer; results usually take 2-3 days.
http://thehealthyhavenblog.com/2010/09/21/suggested-uses-for-geranium-essential-oil/
In addition, you may wish to consider homeopathic remedies Nat. Mur and Kali. bich which are a biochemic tissue salts that serve to help maintain the body's water balance and address mucous levels and congestion. Herbal ingredients such as Pulsatilla and Glycyrrhiza glabra (Licorice) can help to reduce inflammation by stimulating the anti-inflammatory hormone, cortisol, while at the same time supporting the immune system.
http://www.nativeremedies.com/petalive/ailment/cats-dogs-sinus-infections-remedies.html
It's important to support your dog's healing by keeping him warm - warming his food will help in this endeavor and may have the added benefit of loosening mucous. If a vaporizer is not available consider a steam bath in your bathroom by filling a tub with steaming hot water and adding your essential oil to that.
More ideas here:
http://www.vetinfo.com/home-remedies-for-sinus-infection-in-dogs.html
There can be many reasons for dogs to have nasal discharge - ranging from simple sinus infections to major issues such as nasal cancer. If you do not see results within a week of using home treatment, please consider returning to your vet for additional work ups to rule in or out funal infection or bacterial infection or other.
Good luck!
Geranium Essential Oil
Geranium Essential Oil