It's harder with the slim to blow out the atomizer since its connected directly to the battery. What I do is stuff a piece of tissue into the atomizer end and put my mouth over the end with the tissue in it. Then I take a nice draw without pressing the button. This makes the few drops in the atomizer come out into the tissue. Switching flavors after doing this makes the previous flavor disappear faster.
You could always go all the way and take the atomizer head out completely and wipe the inside of the cone down with tissue. A drop of the new flavor right onto the atty head after reassembling it and your good to go.