We recently had a bit of fun trying to see how easily we could pour it out - followed by seeing if you could pour it back in. Solution found:

When pouring it back in to the bottle, you will see bubbles pushing the marble out of the way, and then watch as the liquid runs down one corner of the bottle - it will not fall straight down the middle.

If you hold that corner upwards when pouring, it should pour slowly at first, then smoothly from then.