To maintain you macports repository clean and without unused stuff, proceed with:
port clean --all all
sudo port -f uninstall inactive
If you can’t wait for the clean one to run in the background, there are a few commands you can run manually and faster.
Remove leftover build files (this is done automatically by default):
sudo rm -rf /opt/local/var/macports/build/*
Remove download files:
sudo rm -rf /opt/local/var/macports/distfiles/*
Remove archives (these aren’t created by default):
sudo rm -rf /opt/local/var/macports/packages/*