Get a big tarp (8X10) before you dump anything in the bed hook the edges of the tarp to the sides of the bed or tuck the back corners in the tailgate and the front corners in the toolboxlic (if you have one) When your ready to dump -- un hook the tarp, pull it back a little so the edge is at the back of the gate, climb in and grab the FRONT corners of the tarp and pull like he** The whole load just rolls right out.
Remember to layer more tarps in the load if you have a lot to haul. Ive been doing this for a few years now. It's fast, cheap, and easy
Sorry I don't have any pictures