Or use a website that has an Anonymous Drop Box. Wikileaks did have one, but its no longer operational. I think a few mainstream media organisations copied the idea and claimed to have anonymous drop boxes?
e.g New Yorker has one, called Strongbox - http://www.newyorker.com/online/blogs/closeread/2013/05/intr... - powered by Tor, designed by Aaron Swartz and others, and open-sourced as DeadDrop http://deaddrop.github.io/