I've never seen a 3 day pass, although one can exist. IMHO, if you're going for 3-4 days, you might as well purchase the AP or the Fun Card (if available).
Actually, I just checked the Sea World website and they aren't selling 3-4 day tickets. The closest is the Orlando Flexticket, but that includes other parks. I still think you're better off buying the Sea World AP For $85 or the Fun Card for $52.
My husband purchases the Silver passport, (free parking, discounts on food, souvenirs, paddleboat rides, and on the fish to feed the dolphins, etc) and the rest of us purchase the funcard. Just returned from Seaworld and was a good investment.