Best/Legal way to charge tenant for heating oil in MA

[Conor Meehan]

I'm wondering the best/standard/legal way to charge new tenants for heating oil in Massachusetts and how to incorporate that into the lease. 

Is it best to charge tenants for oil in the tank upon move-in and then reimburse or charge for the difference upon move-out?  Is this legal? (law only allows to charge for 1st, last, security dep and lock fee, but also allows you to have the tenant pay separate utilities if written in the lease).

Or is it better to agree on the amount in the tank upon move in and require them to leave at least that much or pay the difference when they move out?  My worry with charging them at the end of the term is you're more likely to have to chase the money down as they leave.   Can you legally take it out of their security deposit if you write it in the lease?  

Thanks for any advice.