ProLine Series Frost Free Anti-Siphon Sillcock. Offers an excellent alternative to standard hose bibbs in areas where freezing happens regularly through the year. When installed properly in basements or crawl spaces, the valve is angled down slightly to ensure water drains properly when shutoff so when freezing weather sets in, no water is present to cause bursting. The installed anti-siphon will prevent water from backflowing into the valve upon shutoff.