If you're using a self-service soda machine to fill up your fountain drink, you NEED to do this first.
Ryan Seacrest shared the hack that is a must if you're getting a soda at a fast food restaurant. A lot of places will let you fill up your own soda at the machines, but before you pick your drink...
TAKE A NAPKIN AND WIPE THE INSIDE OF THE CLEAR SODA NOZZLE (usually Sprite or 7-up)
If it comes back brown, they probably swap it with another drink, but it means they don't clean it right... but if the napkin turns pink or orange, it's slime mold. Ew!