You Are responsible for daily transfers of engine room bilges. You follow the sequences aft –fwd (P)-fwd(s) bilge well n u have never experienced a problem but 5/E started the transfer n first transferred forward (s) bilge well n without any problem n u join him later u find that bilge pump is not taking suction fr f(p) n aft bilge well n then u have checked everything is normal. What is the cause?