Also could refer to a method of
smuggling crack (and, I suppose, other
freebase form illicit drugs) into
America.
What they would do is, in South America or wherever the coca is being grown, the factory (or something) that makes the cocaine into crack would actually heat the stuff to incredible temperatures, and then mold it into the shape of a PVC pipe. You know, the thick plastic pipes installed nowadays for hot water heaters and washing machines and stuff?
So, anyway, they'd load boxes of the crack pipes onto freighter jets bound for the USA. The drug sniffing dogs at the airport would obviously flag the pipes as being suspect, but upon the customs officials examining them, they would just find...PVC pipes. They were even marked and packed with styrofoam. They didn't look suspicious at all. The official would pick one up, sniff it, look at it, nothing wrong here. It's a just a PVC pipe, only it's made from solid crack cocaine.
Once in the country, it would be sold to dealers or kingpins or whoever's in charge of that sort of thing. They would just use a large metal object to break it down into sellable pieces, and voila, another few grams of crack on the streets of Los Angeles...