That there would depend on the pump and the skill of the operator. Some pump operators have little tricks and gadgets that they use to minimize the mess and clean up time. Others not so much.
With some of the big boom pumps they'll throw some plywood on the hopper grate and pump away until nothing will come out the end of the hose then I've seen line pump guys make a gigantic mess. But if the mixer driver and pump operators work together and communicate the mess can usually be minimized.
Hope that helps.