Meth is usually what you need to avoid. Meth is totally toxic and can not be cleaned or removed from a house. They have to take the dirt with them. I have heard of legislation involved with possibly disclosing meth, but never with crack. Once you find the property, contact the local law enforement. They can probably tell you if there were arrests or calls. You can usually ask people in the neighborhood too, but you might get speculation instead of facts. To get accurate information, you need to hire a professional. Do this at the beginning and pay the money to be sure. You can test/inpsect during the time you have any normal inspections done on the property, once it's under contract. It's worth knowing even if you have to lose your earnest money to not buy a problem. Companies that test for mold, Radon gas, or HAZMAT certified testing can tell you the truth. Right now the only setback with crack houses (usually in cities) is that the junkies will still come by looking for the drugs.
On final note, if you buy a home that is not on owner occupied, disclosure is almost impossible. You will never really know happened. This is true for foreclosures, investor owned, REO, bank owned, and auction homes. You will get a great deal on the price, but REALTORS are not supposed to speculate on what they don't know.