Show Custom Post using Order by

<?php
$post_type = 'custom_post_type';
$post_tax = 'custom_post_taxonomy';
$posts_per_pag = 4;
$tax_terms = get_terms($post_tax, array('orderby' => 'id', 'order' => 'DESC'));
if ($tax_terms) {
    foreach ($tax_terms as $tax_term) {
        $args = array('post_type' => $post_type, "$post_tax" => $tax_term->slug, 'posts_per_page' => $posts_per_page, 'paged' => $paged);
        $t4b_query = new WP_Query($args);
        if ($t4b_query->have_posts()) :
            while ($t4b_query->have_posts()) : $t4b_query->the_post(); ?>
                <div><!--SHOW CUSTOM POST ITEMS --></div><?php
            endwhile;
            getpagenavi();
            wp_reset_query();
        else : ?>
            <h2>Not Found</h2><?php
        endif;
    }
}
?>