All you need to do is sweep up any mess from students at the end of day, and you'll be getting 5 galleons each school day you do this! It will likely have to be done using Muggle equipment only however, so don't try any fancy spells unless you want singed hair and to suddenly be 50! I'm accepting 3 second years for this and no more! Leave an application as to why you think you're best suited for this and then wait to see if you get picked!
(OOC: RPs WILL be needed for this, but it gets you posts, galleons, and it's not too tricky, so why not?)