Apple - How do I manually uninstall the Developer Tools?

Yes, simply run the following in Terminal:

sudo <Xcode>/Library/uninstall-devtools --mode=all

Where <Xcode> is the default installation of Xcode, typically:

sudo /Developer/Library/uninstall-devtools --mode=all

Based on your OP, I am assuming you are running pre-Lion Xcode. This is covered in the documentation that comes with the Developer Tools install:
/Developer/About Xcode

Uninstalling Xcode Developer Tools
To uninstall Xcode developer tools on the boot volume along with the directory, from a Terminal window type:
$ sudo /Library/uninstall-devtools --mode=all

To remove the underlying developer content on the boot volume, but leave the directory and supporting files untouched, from a Terminal window type: $ sudo /Library/uninstall-devtools -- mode=systemsupport To just remove the UNIX development support on the boot volume, but leave the directory and supporting files untouched, from a Terminal window type:
$ sudo /Library/uninstall-devtools --mode=unixdev

Finally, to just uninstall the directory you can simply drag it to the trash, or from a Terminal window type:
$ sudo /Library/uninstall-devtools --mode=xcodedir

NOTE: The uninstaller that ships with previous versions of the Xcode developer tools will not clean everything off of your system properly. You should use the one installed with these Xcode developer tools.

Pleae super-double check that this documentation either exists with your installation or is the same as your installation before you act. As with any such commands, precision and compatibility are critical.