title: Django/PostgreSQL manage.py flush error. look at output of 'django-admin sqlflush'
body: <p>Build: Heroku Python server, Postgresql 10.4, Django 2, wagtail 2.1</p>
  
  <p>I'm trying to essentially destroy and recreate my app DB on Heroku. Here are the steps I've followed:</p>
  
  <ol>
   <li>create db dump (success)</li>
   <li>rm all migrations and recreated the 'initial' migrations (success)</li>
   <li>run `heroku pg:reset DATABASE` (success)</li>
   <li>push new migrations and db dump (success)</li>
   <li>run `heroku run python manage.py migrate` (success)</li>
   <li>run `heroku run python manage.py flush` (**failed**)</li>
  
  </ol>
  
  <pre><code>JVsquad$ heroku run python manage.py flush
  Running python manage.py flush on ⬢ my_app... up, run.2459 (Hobby)
  You have requested a flush of the database.
  This will IRREVERSIBLY DESTROY all data currently in the 'my_app_db' database,
  and return each table to an empty state.
  Are you sure you want to do this?
  
      Type 'yes' to continue, or 'no' to cancel: yes
  CommandError: Database my_app_db couldn't be flushed. Possible 
  reasons:
    * The database isn't running or isn't configured correctly.
    * At least one of the expected database tables doesn't exist.
    * The SQL was invalid.
  Hint: Look at the output of 'django-admin sqlflush'. That's the SQL this command wasn't able to run.
  </code></pre>
  
  <p>My 7th step was going to be <code>heroku run python manage.py loaddata db_dump.json</code> but it also failed, because the flush won't work.</p>
  
  <p>HELP PLEASE</p>