Thanks! Although my setup is different than the picture, (it has one tank for both pumps).The dump valve is indicated by the arrow. It will be on the other side of one unit as there is a LH and RH unit. The pin is either pushed in or pulled out opposite of the current position. When in bypass mode it keeps the check valves open.
View attachment 68260
View attachment 68261
So check your owners manual for the one used by Grasshopper.