Leaking Heater Core

Good news folks. I just finished flushing the radiator. I bypassed the heater core because it is new and I did not want to foul it. The water was dirty but not as bad as I would have assumed. I started by draining the old fluid. Then I rinsed with water. Then I added the flush and water. I ran it for 30 minutes instead of the 10 in recommends. Then I drained again added water. Ran again for 15 minutes. Then I rinsed again with clean water and everything seems pretty clean. I am letting it air dry for the moment. Then I am going to put the new heater core new heater hoses and hope that everything is good again.