the main objective is to remove the "crusty" stuff with an inert solution. that's why we suggest plain saline (contact solution - just the cheap stuff). when applying it to your piercing we want it to be isotonic and pH balanced with your body as to not disrupt anything.
however you find best (but, still gentle) to get the crusties off will work. we suggest saline on a qtip and saturating the crusty stuff then removing it with another q tip. we don't using cups and soaking the piercings because of the risk that the cups have soap residue or something from washing.
the problem with sea salt is even if you get the mixture PERFECT - it's still not isotonic or pH balanced. and you also have to worry about whether or not your water is sterile or the cups are without soap residue, etc.
hope that helps. let me know if you have any other questions.