In order to do this properly, you're going to need a rain barrel. If you don't have a rain barrel then you'll just have a tube running from your gutter onto the ground spewing water everywhere and then your neighbors will say, "What a strange person. Why did they replace their gutter spouts with that length of tubing?" I got mine for free from a nearby plant that was closing down (I know, I know, I know, you're supposed to use food grade. Relax, it held soap, nothing caustic or overly harmful. I rinsed it out very thoroughly). Of course, many of you don't live near old soap manufacturing plants so I've provided a link
for you that has three popular vendors for this particular item. It's really just the search query for 'How to make a rain barrel' again, but every time you click on one of those links an angel gets his wings, and Instructables gets a dime.