Normally a navel won't excrete pus unless it's infected. The whitish/yellowish/clearish excretion coming from a fresh piercing is normally lymph, which is the white blood cells and dead skin of the body, and is perfectly natural in a healing piercing. When it dried, lymph forms the crusties that you'll get on a piercing. If your navel piercing is excreting pus, see your piercer immediately.