People often ask why ashtrays are still placed on airplanes, particularly in the lavatories. Many airlines in operation today have removed them from individual seats as smoking has been outlawed for passengers on domestic routes in the United States beginning with shorter routes in 1988 and progressing to all routes in the 1990s. Smoking was halted forward of the flight deck door a number of years later. Still we see the ashtrays in various locations and the illuminated signs as well. Many of those signs have been repurposed for electronic devices, but that is for another post.
The simple reason that ashtrays have remained on aircraft and, in particular, the lavatory is that there needs to be a suitable place to extinguish a lit cigarette should a passenger feel that regulations don’t apply to them. The trash can is certainly no place for one and the aircraft’s plumbing isn’t either as clogs and other damage can occur. As the most likely place for someone to light up is the lavatory, that is where they commonly remain. However, many passengers simply use them as mini trash cans.