Before Delete Post

by

There’s a trash post hook

add_action( 'trash_post', 'my_func' );
function my_func( $postid ){

    // We check if the global post type isn't ours and just return
    global $post_type;   
    if ( $post_type != 'my_custom_post_type' ) return;

    // My custom stuff for deleting my custom post type here
}