bids are invited for custom bid for services operation and maintenance of effluent/sewage treatment plant excavation for installation of pipes upto depth of 4 feet at starting point and gradually increasing the depth to 8 feet at the ending point (giving downward slope from starting point to end point). supplying and laying of dwc (double wall corrugated) pipes made of hdpe (high density poly ethylene) for sewer line of inner diameter 10 inch, as per sample kept at school premises) and leveling of ground post installation. installation of connecting line from quarters to main line at serial 1 above, dwc (double wall corrugated) pipes made of hdpe (high density poly ethylene) with inner diameter 6 inch (installation includes excavation of ground, maintenance of proper slope and leveling of ground post installation). construction of manhole chambers of size 3 x 3 x 3 feet (approx) with cover and step (if required as per site condition). construction of manhole chambers of size approx 5 x 5 x 5 feet with cover and step (if required as per site condition total quantity :