According to the Fish Channel, dead goldfish can be disposed of in a variety of ways that include burning the remains, burying the remains in a garden or placing the remains in a trashcan. It is important to wrap the goldfish remains in newspaper or plastic prior to trash disposal.
It' dangerous to flush dead goldfish down the toilet, and doing so is never recommended. Flushing a diseased fish can cause harmful bacteria and organisms to enter external local waters, which in turn can cause disease outbreaks among local fish. It's also important to ensure that the goldfish is fully deceased prior to disposal. Fish are considered deceased if at least 10 minutes have passed since the last gill movement.