It's can be very frustrating trying to get the last traces of a liquid product out of a bottle, especially if the product is expensive, sold in a pump bottle with a short tube and/or cannot be heated or diluted. I use a couple spare caps from empties* to make connectors that allow me to transfer the contents of a nearly-empty bottle to a nearly-full bottle. This method works on products you use regularly - because they have identical caps and bottle sizes. If you know what the toy "a tornado in a bottle" is, this connector will seem familiar. You can leave the bottles connected, unattended, for as long as necessary without worrying about them being knocked over. The connector can be reused indefinitely as long as you are careful about not drenching the duct tape when you clean it and as long as the manufacturer doesn't change the packaging/cap size.
*To get started, you actually need only one spare cap, because you use the cap from the nearly-empty bottle you want to empty and discard as the second half of the connector.
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