On the bottom of any plastic container will be a triangle formed by some arrows with a number in the middle. That will identify the type of plastic you have on your hands.
The "best" for our purposes is "#2" or HDPE, which is what all those ubiquitous white 5-gallon buckets are made of and is also what Starboard plastic is.
http://www.americanchemistry.com/s_p...5&DOC=FILE.PDF