Not so long ago, we simplify registration process at our site leaving only the username field...
As a consequence, we are faced with a problem of creating multiple accounts by the same user and abusing faucet (faucet at our site - 0.007 mBTC and only request every 3 hours when balance is zero).
Guys, what solutions do you recommend?

Thank you!
Your gambling site must have a system that will detect same IP registrations. I think it is being used by some gambling sites because I already experienced having banned for faucet or chat when I make a ticket to support and ask why I am banned, they checked my IP and they saw may users are attached on my IP. Although i just have 2 accounts (they allowed it) they says I have more than 2 accounts thats why they banned me.
I never use vpn by the way.