The dreaded Plastic hose leak.
If tightening the fitting fails, then you need to replace the line.
Remember tight is tight and too tight is bad, so don't break anything.
Uncle "Richard" Douglas has a Land Rover with big wheels that never gets stuck... until he breaks something so it won't go. Uncle Douglas always breaks something. - Anna Crowther at the Conclave 2012 (AKA Carburetor Neck)