I would like to dig a drywell to handle my basement sump and my gutter drainage. digging down i hit sand at 4'and the size of the well right now is 3'x3'. my question is on the type of stone to use(p-gravel,3/4" stone..ect). Dimensions of the well and should the stone be layered with something to keep the dirt out. Also should the drainage pipe extend to the bottom of the well.