Chimney pipe

Trevor is dead right. the seal is unimportant. as soon as there is hot air rising through the pipe any not perfectly sealed joint will only be sucking room air INTO it not out.
Basically once the draft is established the hot air rising up through the chimney is MOVING AIR. the air in the fireplace room (My rec roomin my case) is static air that is barely moving at all at best.
Air in motion exerts less pressure thna air not moving so therefor the non moving air will flow INTO the imperfectly sealed single wall stove pipe joint and go up the chimney. In itself that is actually desirable. it is less efficient as a means of heating BUT it makes it impossible for carbon monoxide to enter the house. Unless i'm stoking the fire i cannot smell my woodstove because all the airflow having combustion applied to it is being fed up and out.
I love the fireplace smoke smell but i like living my driveway and porch smell like my fire my house does not due to the partially burned products not entering the house itself