Our 05 Wildwood doesn't even have such a valve. We use a compressed air adapter and attach it to the hose connector for city water and attach a small air compressor and blow out the lines via the faucets. So, if you are not able to get yours fixed soon, one thing you could do is go to Walmart or your RV supply place and get the schrader valve adapter (made by Camco I believe) and do it that way. As our air compressor will put out more than 40 PSI, we also use a brass pressure snubber in series with the air adaptor to prevent overpressurizing the plastic lines.
Don't know if any of that will help you, but it is an alternative to putting anti-freeze in your lines.