Vacu flush runs intermittently

[rcwiegand]

I am on an extended trip and noticed the vacu flush will cycle without flushing.   This may not happen for days then it will begin and occur a few times before it stops.  When this happens the pump cycles about half the time it does with a full flush.   It seems to occur most often in early morning when it is cooler. There is always water in the bowl when it happens.  I recognize there must be an intermittent vacuum leak and looking for suggestions where and how to start.