I had to come up with a locking system and here's my method: A close top drum, the best kind has 2 wide 2" bungs, and 1 smaller 3/4" often they're industrial polymer barrels. In 1 of the 2 wider bungs fit a standpipe (barrel drum) pump. A standard duty pump will do for veggie oil but one with some weight. Then if you have a center bung you can adapt this with a spout and locking cap, otherwise you have to adapt the smaller 3/4 size up to accommodate a locking cap and the ability for a restaurant to pour into the spout with a funnel. All fittings can be secured with JB weld, or welded.

This clearly won't stop a determined thief but here just about any attempt can be considered felony B&E. My restaurant owner was more than happy to involve the law if it came down to it. They were also happy to keep a key to the lock.

It also makes collection super easy and electric free. It's ironic in my very small town, 2 years ago this wasn't even a remote concern. But now there's a thief siphoning directly into his tank without filtering; Karma is a lesson! But surely there are more and better methods out there; it has come time to stop the thieves!