My tank is a Phototax Model 20. It has four parts: the tank proper, a funnel, a gasket that goes between the tank and funnel, and a lid with a "pressure release valve." It's been years since I've used it. It seems to be light tight only when the lid is on. The funnel does not have any sort of light trap, so it would seem you need to be in total darkness when you add or drain any liquid. Kind of a pain. My original tank, which disappeared decades ago, had a light trap in the lid that allowed liquids to be added or drained without opening the tank. I'm wondering if I'm missing part of my present tank?