Effective use of co-disposal of waste rock and tailings depends among other things of the use of a high slurry solids concentration so as to minimize segregation of the finest particles. Generalised large-scale loop-results from the GIW Hydraulic Testing Laboratory, U.S.A., have here been used to demonstrate the economical potential of pumping at high solids concentrations with centrifugal pumps thus reducing the costs for pipelines, energy and water recycling.