I've never known what it means. I G**gled it, but don't see any relevant results, as both words are commonly used in other non-sexual contexts.
No sexual slang or urban dictionary has a listing for it either, as far as I saw.
Thanks.
It's when you back your truck, or trailer up to the designated location, ingage your PTO, unlock your gate pins, and raise the body until the contents slide out into a pile, or into a trench, depending on if it's excavation or materials hauling. To really get that load out, especially if it's sticky, you need to sort of pop the clutch to lurch forward, then immediatly slam the brake, causing the gate to slam hard against the body, to loosen that sticky load from the floor, and make it slide out. The same basic operation is used to dump a load from a dumpster also, but it would be in a land fill, and not a job site. I hope this helps.