They are serious about this in Germany. At the Christmas markets it's common to get a single Glühwein mug that you keep and have filled with drinks as you visit

They are serious about this in Germany. At the Christmas markets it's common to get a single Glühwein mug that you keep and have filled with drinks as you visit. Even these little souvenir keepsakes have a fill line marked on them, no doubt policed by some very stern German standards keepers.