When you're applying caulk, you almost always apply more than the amount you need, then smooth it out, leaving this blob of caulk that's messy and goopy, and you have to just throw away. It's wasteful, and you usually end up with half of the caulk from the tube being wasted this way.
My invention is a kind of caulking gun that operates in reverse: instead of pushing the caulking out of the tube, it sucks it back into a tube, like a medical syringe. Then with the flip of a lever, you can squeeze it back out for your next caulking job. I figure it can save probably 50% in your cost and eliminate waste, so it's both fiscally and environmentally friendly.
I'm calling it The Caulksucker.
Next up: a set of small flasks in the shape of golf balls so you can surreptitiously carry shots of your favorite sippable alcoholic beverages out on the golf course. I figure I'll call them the Ball Liquor.