Scripts Importing and Authentication

The Postgresql I use is configured to authenticate users via md5
(trust option in pg_hba.conf file)

These days, after pg_dump'ing a database, and then reimporting it,
Postgresql asks for the password of every user which is described
by the \connect command in the script. I have used the environment
variables PGUSER and PGPASSWORD, but they work for only one user,
and the script has about 4 users in it and I don't know which
one of them Postgres wants to know, because it only shows the
prompt saying 'password:' and nothing more.

So, is there a way of making the import of a script without
having to supply passwords of all different users contained
in that script? (I haven't done that, I have disabled the
authentication)
Is there a way of making it without disabling the authentication?

Thanks.