Can’t help with the tea, but a former 609 Squadron rigger told me how their custard was regularly laced with cascara (hope I’ve spelt it correctly) “to keep us regular.” However, he said that they never stirred it in, so, if they saw an oily film, on top, they would swap their bucket for that of the Sergeant’s Mess. Apparently, the sergeants never understood why they spent so much time in the toilets.
Edgar