A plug for sealing a bore in the wall of a high-pressure fluid container is provided. The plug includes a sloping surface adapted to seal at an edge between surfaces of different diameter. A method for sealing the bore by forming a socket in the wall that is adapted to receive the plug is provided. The socket may be formed by reaming a tapered hole to form a surface having a minimum diameter greater than the diameter of the bore and tapping a segment of the tapered hole. A ball may be forced into a cup of the plug to increase radial force between the plug and the socket.