An apparatus and process for removing and recovering contaminants from a pipeline while containing and preventing the contaminants from spilling or leaking into the environment during said removal comprising. The hosts store for each multicast group an included source record and an excluded source record, and the network interfaces of the hosts send to the router a message containing information about the included source record and information about the excluded source record. Output of one FIR filter is subjected to reverberation adding processing by the reverberation adding circuits and then output of yet another FIR filter is added to the above output to obtain an output signal.