All tanks stainless steel or Plastic and particularly reels pick up a trace of gelatin each time you process films, it pays to bleach them in Sodium Hypochlorite (household bleac) ever 6 months or so, I follow that with a good wash in washing powder - biological if there.s some around, then scrub the reels with a toothbrush It's this gelatin that retains traces of wetting agents etc.

Ian