Post slider with custom post type

I don’t have enough rep to comment, but what does your actual query look like?

Edit: I haven’t been able to test it, but I think this will work

    $args = array(
        'post_type' => 'slider',
        'meta_key' => '_thumbnail_id', // only pull sliders with images
        'tax_query' => array(
            array(
                'taxonomy' => 'slideshow',
                'field' => 'slug',
                'terms' => 'homeslide',
                'operator' => 'IN'
            )
         )
    )

$query = new WP_Query( $args);

Then follow the normal loop