Renovating our northern Michigan cottage bathroom. I wish to install a whirlpool tub. Noted that the pricier units boast 100% draining (pipes and motor). But more reasonably priced units which I prefer, e.g. Sterling Plumbing (Kohler's Economical brand), do not state this draining feature. I will blow out the copper lines, but am wondering if water becomes residually trapped in these other tubs making them a poor choice. Any thoughts or experience on this. Very cold climate in winter. Thanks!