After building a database using an ill-judged algorithm, I ended up with junk in the database that consumed 600MB of space in the Postgres data directory. Deleting the bad data did not free this space immediately, and I was too impatient to wait for the auto vacuuming to kick in.
Here are the steps I took to clean up the database and data directory -- with extreme prejudice.
In the psql console:
VACUUM FULL VERBOSE; REINDEX DATABASE mydatabase;
On the command line:
Running all of these steps is a brutal process. Do not run the
command if you have important data, because you will probably want to keep your
write ahead log.