We have discovered that the vacuum breaker/check valve under the bathroom sink in our 29RKS leaks when the water to the black tank flush is turned off. Has anyone else ever experienced this? I looked up the valve on the internet and discovered that it is common for it to leak and a lot of people replace it with a brass version. It is also a pricey little thing at $60+ . I called my dealer today and made an appointment to have it repaired. I just hope the dealer will install the upgraded version and not another one of the faulty valves.