The domain name Plumber.com has been registered since 1995, being created on the 3rd of January 1995, it appears to have been in the ownership of Roto-Rooter since at least 1998, where we can see the first developed website on Plumber.com archived online by archive.org.
Who is Roto-Rooter, well they can trace their history back to 1935, 60 years before Plumber.com was created, The company was founded by Samuel Oscar Blanc and today has a nationwide service across the USA and also operates in Canada with over 3,600+ employees.
The company has a few other nice names in its domain name portfolio including rapidplumber.com, proclean.com & anydrip.com, you can see the full portfolio below.