I use food grade DE. I put it in their feed and sprinkle it around the hen house. I have never had to 'worm' my chickens with medication type wormers. Cynthia has a pumpkin seed and buttermilk recipe for worming so maybe she can chime in here and give you the how-to. Both of these work and are natural solutions and you don't have to wait to eat your eggs. edited to add: I put it in the feed all the time. It is not an occassional thing or just for worming. When I am mixing grains or commercial feed I mix it in then so it is present at all times when I scoop and fill the feeders. Sometimes I even add a dash their treats.
I do put DE in their food maybe every other fill up and on occasion give them a bowl with buttermilk, pumkin seeds and yogurt, etc. These are more of a preventative thing and depending on what may be in your soil, among other considerations, you may at some point have to use a chemical wormer. From what I can see there are basically two choices that do not involve a long withdrawal period-Eprinex Pour On and Levasole (or is it Levamisole? My mind is a blank on the spelling). One is basically a cattle womer with no milk/meat withdrawal and one is a pig wormer with a seven day withdrawal. Unfortunately, as far as I know, no broad spectrum wormers are available for chickens that are laying eggs, approved by the FDA. Piperazine only zaps roundworms, one of many types the birds can get. The best thing is to try the preventatives on a regular basis and stay vigilant to what is going on with the birds. You may never need to worm them chemically, although many people have other opinions about that. Some do it regularly, no matter whether they think the birds have a worm load or not. I'm not saying what's right and wrong on the worming question, just offering up what I know about the least offensive wormers as far as withdrawal times for eating the eggs again.