Once you've poured in the new oil, pour the old oil into the empty container, or an extra one you've bought just for old oil. Your local waste station/refuse tip will take it, some mechanic shops do too. There's a small fee on weight as they will process contaminants out and what's left is recycled for plenty of stuff.

I usually unload once a year or so when I've got 2-3 containers piling up. It's as simple as pouring it out into their big tanks and recycling the containers there or taking them home to use again.