Cleaning port’s garbage
portsclean cleans garbage from the directory tree of the ports collection. It is a utility of the base system that should be run from time to time to keep one's ports infrastructure as sane as possible.
portsclean wipes old package files, unneeded libraries and such. There are several interesting option flags described in the man page. This is how I run portsclean from time to time:
% portsclean -DD
The command above cleans all the distfiles that are not referenced by any installed package in the system. I usually run this after rebuilding the complete userland from a new ports fetch.