Originally Posted by lbdils
Ron, OK I re-read your reply and I think I get it. The vacuum breaker under the bed allows air in (1 way) to let the vent on the roof work properly (air/gas out).
You are correct, that is part of there function, the other part is to allow the water to drain down a pipe without vacuum (negative pressure) slowing it down.
Many of the stationary homes now have them installed, our home base does. We have one under each sink in the bathrooms and kitchen as does our motorhome. They do the job as the name implies, Vacuum Breaker. They do not let a vacuum built up in the lines and thus the water ETC. drains down the lines faster.
If you do have a bad one, they can be purchased at Lowe's or any plumbing supply.