How do I clear/truncate/delete BIBlend tables?

I have some BIBlend tables I have created during testing of a Workflow. that I want to delete/Truncate

Resetting the Scenario doesn't do it.

Do I need to do it programatically or via a Data Management job? When I try this it tells me that the SQL is not safe (I have tried with TRUNCATE TABLE and DELETE)

Thanks

Steve