I agree with Myrna M, because it surely could be a or respiratory infection. Such kind of infection are not good at all and might kill your pet dog. I suggest a quick visit to your local vet before it's too late to save him.
Your complete post didn’t come through for some reason, but dark brown mucous coming out of a warm dry nose does not sound good. That color could come from a combination of blood and infection, which is not a good combination. I’d recommend your ex have the dog examined to determine both the exact nature of the discharge as well as its source. It might be something like a foreign body the dog has inhaled that's causing the problem or a sinus or respiratory infection.
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