Prevent warning about Macports/Fink installation

Question

How can I prevent the following warning from Homebrew appearing whenever I install something?

Warning: It appears you have MacPorts or Fink installed. Software installed with other package managers causes known problems for Homebrew. If a formula fails to build, uninstall MacPorts/Fink and try again.

Note that I've never (that I recall) installed Fink on this machine and I just uninstalled Macports. I've tried removing /opt/local/bin from my PATH to no avail.

Answer 1

Did you follow the official guide? (specially the "rm" part)

Answer 2

Looking at the source (in def macports_or_fink_installed?), it seems to check something like this:

$ which port
$ which fink
$ ls /sw/bin/fink /opt/local/bin/port  # if they exist
$ ls -ld /sw /opt/local                # if either directory exists it must be readable