{HEAD ~ a plurality} of {TAIL ~ plugs} each connected to an associated one of the second pipes, having an internal hole communicating with said associated one of the second pipes, and having a hollow plug body in which an associated one of the sockets is detachably engaged; and 
{ HEAD ~ a plurality } of { TAIL ~ plugs } each connected to an associated one of the second pipes , having an internal hole communicating with said associated one of the second pipes , and having a hollow plug body in which an associated one of the sockets is detachably engaged ; and
HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH