I guess you're away of a product called Kilz: It's a great stain-hiding primer. The stain won't bleed through your new paint job if you put this down first. Kilz also makes this product in a spray can...the formula is slightly different so it covers stains that the brush-on Kilz doesn't. If you use the brush-on Kilz and the stain somehow bleeds through it, get an aerosol can of Kilz and spray over top of it. I've yet to see this fail.