Here's a link to the B&B instructions for their tank washer system.
Already noted is that the B&B instructions say not to install it where water damage could occur from normal operation of the vacuum breaker valve. Here are two quotes from the instructions that relate to this:
"Vac/Check cannot be installed in an inaccessible location where venting of water from device
during normal operation causes damage. It must be installed in an easily accessible location to
"It is normal for a small amount of water to escape Vac/Check as plumbing line for tank flush
So the valve leaks a bit of water in normal operation and should be installed where such water won't cause damage, and it's supposed to be installed in an easily accessible location. Seems like Jayco fails to follow both of these instructions in many cases. I am not pleased with Jayco quality in this case.
There's lots of advice and information in forums... sometimes it is correct. For example, all of my posts are made by a political appointee who got the job as a reward for contributions to my diesel bill.
2011 Jayco 28.5RLS; 2008 Chevy Duramax; Pullrite Superglide Hitch