Abstract: For use in providing back pressure in a slurry flow, a first pipe has an inlet for receiving the slurry and an outlet for discharging the slurry. A number of inverted U-shaped second pipes communicate at their ends with the first pipe at respective, spaced locations along the length of the first pipe. Each second pipe has a pair of spaced sides and each side has an orifice choke therewithin. The sides of each second pipe extend upwardly from the first pipe so that the second pipes are self-draining. A valve is provided for each second pipe, respectively, each valve being carried by the first pipe near one end of the corresponding second pipe. A generally horizontal third pipe is coupled to the first pipe in bypass relationship thereto. Valve means controls the flow of a slurry into either the first or the third pipe.