All, I've acquired an older but apparently in good condition Patterson system 4 tank for a song. Looks clean and free of wear. It doesn't feel solid though. When I twist the funnel on it clicks into place fine but I would expect it to be very tight. It doesn't appear to be so. So... Some questions 1. Is this normal? 2. If it is are these tanks really daylight safe? 3. I seem to recall having read somewhere that the little agitator stem is part of keeping this light safe. Is that true? Any help would be greatly appreciated.