Does your toilet flush tank leak when travelling?

Just taken delivery of a new 2012 Coachman.  Whilst being shown how all the bits work the dealer told us to empty the flush tank to the toilet before leaving site as they can leak when on the move!  Have been caravanning for 15 years with various caravans and have never been given this advice before.  Also never had any leaks either.  Have you experienced any leaks with your flush tanks??