If you can't get the leak to stop by tightening the flare nut fittings more, start over. Disconnect the lines and this time put a little bit of motor oil on the flared part of the tubing (rounded end that meets up with the filter) Now reassemble the lines and get them tight. The FSM actually recommends putting a film of motor oil on the flared part of the tubing and I think it's because it helps the lines mate better and provide a leak-free connection.