Filtering by a column that is on a pivot table

[Hirsi98]

I have two tables post and tag and their pivot table post_tag. I have a grid table on the frontend of my laravel application that displays all the columns from the post table and a column from the pivot table post_tag. How can I filter the list of items of the post table based on the pivot column (say tag_id). All the pivot table contains are post_id, tag_id and status. I noticed the fields to filter by must be specified in the table's model such as post and tag. Thanks.