Be sure to wrap as much as the area you dig out with Filter Fabric. It can be 'had' at a Gravel Yard or Crushed Stone Yard. (THey're in the Yellow Pages under the said labels.) Don't use landscape fabric or week block. The fabric will keep any debris out of the crock/pit but allow water to pass through. Do set it at surface-height in case you need to get at it. Check the paperwork with the pump to be sure of the maximum length the pipe can be. I believe this is a constraint but I'm not sure. It may be, say, 20'. But maybe that's if you're pumping uphill. YOu did say you're on a fairly, level lot.
My best to ya and hope this helps.
PS: Personally, I'd dig out the pit 2' wider than the crock and about 6" deeper than its height, line it with fabric, put in 6" of crushed stone, set in the crock wrapped in fabric, back fill with the rest of the gravel to about 6" from the top of the crock, lay more fabric over the stone (and tuck it down the sides all the way around), back fill to the level of the crock, and plant grass. (Whew!)