There is provided a tubular connector or the like comprising a socket like means and an annular elastic sealing member to be fitted into the socket in pressing contact with the inner peripheral surface thereof. To assist in the assembly of the sealing member internally of said socket the socket and sealing member is each provided with a plurality of marks spaced apart circumferentially thereof in corresponding relation to the other. The sealing member is fitted into the socket by inserting the sealing member into the socket with the marks on the sealing member set to the corresponding marks on the socket and pressing any slack portions or depressed portions of the member against the socket radially inwardly peripheral surface, whereby the sealing member is secured in uniform pressing contact with the said socket inner surface over the entire outer periphery of the sealing member. Alternatively the sealing member can be temporarily pressed against the socket by fastening them together by clamps at the positions where the marks are matched as above, followed by further clamping the resulting assembly at an unfastened portion by means of another clamping device possessing clamping rollers, the said device is moved arcuately with respect of said assembly.