A few sources report that elephants use their trunks to masturbate. This practice, if it exists, is apparently called trunking,

Per todayilearned.co.uk,

This may not be the most useful piece of knowledge, but if you ever get to see an elephant doing this you would at least know what he is up to. Urban Dictionary calls it trunking. Don’t try to do it at home – you will break your back.

They provide some pictures of this practice, but I'm not sure if these are photoshopped.

Do elephants do this? Or, is this all fabricated and the pictures fake?