A Dry Well is simply a deep hole filled w/crushed stone. BUT FIRST, if you're feeding the well with piping, your piping should be layed to the well first. If it's NOT being fed with any piping, then you need a 'drain vent' to stand verticle somewhere in your well as you fill it w/stone. You'll need a 6" piece of flexible black pipe with a vent-cap to go w/it. (Ask the folks at the Store for this. You may need to buy an 8' piece of pipe, and just cut it to length.) The TOP of the vent should be about 1" ABOVE ground level when the well if complete. Of course, as you put stone in the well, you'll need a 'level line' across the top of your well so you know how high to set the vented piece of pipe.
Now that you have the pipe ready, you dig your hole as LARGE as you want, and as deep as you want (minimum 24"), no closer than say 15' from the house (if possible). Then, line it with Filter Fabric which can be found at a Quarry, Stone and Gravel Yard, or possibly a LUmber Yard. Then, fill it with crushed stone 3/4" in size, at about 3" per layer. Tamp EACH and EVERY 3" layer. IF you're using a verticle vent pipe, then at some point you need to 'stand it up' and keep filling. Fill with gravel to within 4" of the top. Then, COVER the top of the stone with more fabric (or the 'excess' fabric you lined the sides and bottom with.) DON'T cut the fabric around the vertical piping (if you project needs one.) Just wrap the excess around the sides of the pipe and vent. THen, throw 4" of soil/dirt/whatever on top and plant grass. You now have a 'clean' dry well!
Now, like I said, I don't know if your well is being 'fed' with any piping. IF IT IS, just plan accordingly. If it's not, still plan accordingly. If you have a vent cap, put a 'leg' from a pair of nylons on top of the pipe BEFORE you put the cap on. This will help keep leaves and pine needles and 'junk' out of your well. Periodically, take the cap off and either clean or replace the 'aging' nylon. Or, if you're feeding your well with horizontal piping from, say ..., your downspouts, then put a piece of nylon on the STARTING end of the piping (where the downspout enters the black pipe.) It too, should be periodically checked/replaced as it ages to keep debris OUT of your Dry Well.
The keys to this are: Lining the well with Filter Fabric. Tamping the gravel every 3". 'Standing up' the vent pipe (if you're using one) to 1" above ground level AS YOU FILL the well with gravel. 'Protecting' the well from debris with the use of nylon stocking.
I did find some info that might help. Do read the whole thing because there is some subtle info about water issues along with dry well info. See Drainage Brief. If you need more info or clarification, e-mail me directly. My best to ya and hope this helps.