and example of this is:
tag=doctor+smallville,receptionist+smallville
so only find doctors or receptionists in smallville
In case anyone stumbles across this, this is how I solved it. I had to use associative arrays. This was the code:
$args = array('post_type'=>"post",
'posts_per_page'=>-1,
'tax_query'=>array(
'relation' =>'AND', array('taxonomy'=>'post_tag',
'field'=>'slug',
'terms'=>tag1,
'operator'=>'IN'),
array('taxonomy'=>'post_tag',
'field'=>'slug', 'terms'=>array('tag2','tag3'),
'operator'=>'IN'))
);
$thepages=new WP_Query($args);