Tks for both reply!

The leaking is occured between the steel piping that connecting to the reservior (not the rubber hose, the rubber hose is perfect.) and I had tighten the connecting nut but still found mositure. I just do'nt know the connector nut contains seal O ring or it was just direct coupling from steel pipe to reservior tank, if it contains o ring, then may be I can try to replace it. Any idea? TKS!