A Float Test is a term given to garbage that is tossed overboard while at sea. The term is used to describe material that is to be discarded in a less than optimally environmental manner. Said equipment is usually described as nfg, and therefore needs to be "Float Tested".
Cpl Smith- "What'd you guys do with that bad radio the CO wanted destroyed?"
Lcpl Jones- "We float tested it over the Marianas Trench."
Cpl Smith- "Very well, carry on."