he may have ear mites or yeast. ear mites cause a blackish,tarry looking crud & itch like crazy. dogs with floppy ears can get yeast infections because inside the ear gets wet & doesnt dry out very well under that big ear flap.you can get meds for either at most pet stores,farm supply store ,& even walmart
Ear mites, infection heavy wax build up. When you bath your dog use a cotton ball in each ear to keep water out. Clean it regularly like we do our own. If not you can have a $$& vet bill. Green Tea Tree oil with aloe ish top suggestion.