The 'secondary drain' youre talking about is a freeze drain or a winterizing drain... I shouldnt matter which jet you stick the hose into, the water will exit that secondary drain.
It would probably be helpful if you had a plumbing schematic- at least this way youd know what lines are tied together. Im sure your HotSpring dealer will have this if they keep their service manuals up to date.
The real key to finding any leak though, is to be able to see the water transfer from the leaking fitting.
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