backup/restore and vacuumdb

I'm doing some migration script from mysql database to an existing
postgresql database. Everytime I want to test it, I want to get the postgres
"destination" database to the same situation it was before the last script
was run.
I am doing a backup with pgdump and restoring by droping the database and
running the script generated by pgdump.

The backup looks like this:
pg_dump -h <hostname> -U <username> -C dbname > /tmp/database.pgdump

The restore looks like this:

psql -h <hostname> -U <username> template1 -c "drop database dbname;"
psql -h <hostname> -U <username> template1 < /tmp/database.pgdump

But this aproach is taking a long time and the database is becoming slower
every time.
So: which is the best backup/restore method to apply in this case? And about
the performance, I'm using vacuumdb but I don't know when to do it. Any
idea?
Thanks

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