PURPOSE: To prevent remaining oil from flowing out from a collecting device in removing a blanking plug again by making a portion covering a connection opening have a range continuous to the sealing part of the connection opening, and filling up liquid absorbing material in the range.

CONSTITUTION: When a connection opening 3 is sealed with a blanking plug 10 while a brake system 1 is being transported from a manufacturer to an automobile maker, remaining oil in the brake system 1 flows into the connection opening at the time of oscillation during transport or a posture change, and moves into a hole 13 through a hole 15 and/or slit 16 formed at a portion 12. The hole 13 is filled with tampon 17, or formed material such as absorbent material, therefore, remaining liquid is absorbed to be stored in the hole 13. Even if the blanking plug 10 is removed again to connect an automotive brake tube or other hydraulic tubing under an automobile maker, therefore, there is no fear of remaining oil flowing out from the brake system 1.