Can I fly with an anal abscess thats not painful anymore?

Why not? If you anticipate a prolonged flight, you may want to speak with your surgeon, or at least employ an inflatable ring ("doughnut") upon which to sit. Considerations also need to include: is the abscess sterile or infected?; is there underlying inflammatory bowel disease (that may be active)?; is there bleeding or oozing from the site?
Sure. As long is it is covered and not leaking.