Good at home strenght workout with only 15 lb dumbbells/pullup bar?

I'm 15 years old, about 6'1 165 lbs. I play water polo and swim so I'm looking to put on mostly strong, lean muscle. I get 2-6 hours of cardio 5 days a week so thats not a huge issue. Whats a good routine with my limited equipment? I would also like to incorporate an ab workout (going for the six pack, almost there) thanks.