One of the frustrations we've found with plumbers is that it's difficult to get a quote, and therefore, it's difficult to know if you're paying a fair price for your clogged drain, blocked toilet or leaking pipe. We called plumbers throughout the US and couldn't find a major chain that would give us a quote over the phone, even for routine work. Instead, the technician needs to come to your home (or business) to give you a no-obligation estimate.
From the businesses we talked to, our understanding is that tipping plumbers is not necessary and is unusual. One phone representative from Roto Rooter told us that he has heard customers call the main office to express how pleased they were with the exceptional service and the quality of clean up.
It appears that tipping is not expected and is not the norm, however, plumbing can be unpleasant and difficult work. If a technician provides exceptionally good service, we've been told "it wouldn't be completely unheard of" to give a tip. The manager at a local plumbing chain said that it would not be against company policy for one of their staff to accept a tip if you so chose.