Sometimes it will be too watery and sometimes they will have true diarrhea. Yeast are not bacteria they are one celled fungi. Antibiotics are designed to kill bacteria. That was made from bread mold which is in the fungi family. Sorry it isn't exactly that kind of a yeast infection.
Birds have one common tract for urine, poop, eggs and sperm.
Yeast infections in birds are equal opportunity infections, males as well as females are prone to them. Baby birds get yeast infections in their crops. Sometimes they regurgitate or vomit. Adult birds can have yeast infections anywhere in their digestive tract. A swab of this area can be tested with a culture and sensitivity or a direct Gram Stain.