A refrigeration system uses a refrigerant which contains, as a main component, hydrocarbon or HFC-152a. A fluid tube, such as, a gas charge port tube is hermetically connected to a refrigerant flow passage in the refrigeration system for filling at least the refrigerant into the refrigerant flow passage. The fluid tube is sealed against leakage of the refrigerant from the refrigerant flow passage by means of a pinched portion and a squashed portion of a flat-plate shape which extends from the pinched portion to a distal end thereof. The squashed portion may be folded at a plurality of portions for enhancing the sealing effect. Further, instead of the squashed portion, an adhesive may be used for reinforcing the sealing effect provided by the pinched portion. Alternatively or with the use of the adhesive, an elastomer may be used for reinforcing the sealing effect provided by the pinched portion.