I have a urinal that over flows on occasion... last sat I plunged it and got out a lot of stuff that looks like green sand... I'm assuming it's a salt or calcium buildup... what chemical can I put in it to clean this out and make it work properly.

I found something that's just made for your problem called UrilX.
UrinX II Urinal Cleaner
Designed not only to remove the calcium deposits caused by urine, but with regular use, helps prevent urine build-up in Portable Restroom urinals and on the floor
Check it out at, http://www.jjchem.com/productlist.aspx?subcatcode=15
Good luck, Tom