What type of fitting is there coming out of the tank? If it is a flared fitting, loosen and tighten it several times while watching where the wrench ends up on each tightening sequence to observe a slight increase in degrees turned. This process will avoid over-tightening, while at the same time, causing the flare to make a very secure fit with the female inverted flare fitting.
If it is a clamped-on hose, make sure that the hose is new and is a snug fit before the clamps are tightened.
