You can then take your gas line and connect it into the fitting. Push the hose completely into the fitting, and then hold it in place by turning the fitting seal with your fingers. If you are adding several lines at once, attach the hoses and seal lightly before starting to seal the connection using a wrench. In some types of propane tanks, such as those used in boats, it is necessary to attach an adaptor to complete the seal. This can be in the form of an O-ring or similar connection. Tighten the O-ring first, and then attach the propane tank fitting over the top. here