Will the seals in a toilet dry out if the water is disconnected for a long period?
There are several things to do before leaving a house for a year.  Try a quick search for "winterize a house" or something similar to find many checklists.  One list I saw mentioned pouring RV antifreeze down each of the drains to fill the P-trap, then putting stoppers in the drains and plastic wrap in the toilet bowl to help keep it from evaporating.