Ok figured that out for the most part. Now it's still truncating the description. I've taken out the zen_trunc_string part and now my string is like this:

/*zen_trunc_string(/*zen_clean_html*//*(*/stripslashes(zen_get_products_description($listing->fields['products_id'], $_SESSION['languages_id']))/*)*//*, PRODUCT_LIST_DESCRIPTION)*/

or with the comments taken out: stripslashes(zen_get_products_description($listing->fields['products_id'], $_SESSION['languages_id']))

However it's still truncating the product description.