We used to smoke on my crew on the Valiants without any problem. We had to; being on tankers we had to rid of our surplus duty free. Wheels up, fags out, was the call. especially after the hour it took from leaving ops to getting airborne. We would use one of the cups with a splash of coffee as an ash tray. At the end of the trip, to hide the evidence, we would depressurise during the approach and I would open my DV panel. Then I would hold up the cups in turn and the contents would be sucked out to be consumed by No 3 engine.