Nutone central vacuum leaks brown liquid

\015 I have a Nutone central vacuum in our home and we have not used it in months. When we run our dishwasher, the vacuum ports have strong suction. And the vacuum is never even turned on. One of our ports has started to leak brownish greenish liquid. Again all of this is happening and we don’t even use the vacuum system. We switched to an upright vac several months ago when the vacuum system was clogged and stopped working. Any help? Thanks\015 – Broan-NuTone Vacuums