Self-draining. Mansfield anti-siphon frostproof sill cocks assure protection against freezing and undesirable back-siphoning. Because they're frostproof, they can stop outside hydrants from freezing and bursting the pipes. Plus, the anti-siphon feature protects against water siphoning back to contaminate the potable water system. Also, unlike anti-siphon attachments, which must be manually drained to prevent freezing, the integral anti-siphon design is self-draining. 1/2" sweat inside, 1/2" I.P.S. outside.