How do I drain sauerkraut?
At every restaurant I've ever worked at we warmed the sauerkraut on the griddle while the bread and meat were grilling. This evaporated much of the moisture in addition to making sure the sauerkraut was warm enough to not make the sandwich cold.

So we'd have the sandwich warming up open faced, cheese on each face. Then meat and sauerkraut would be warming individually. Once the bread was crisp and the meat/sauerkraut were warmed up you'd place the meat one piece of grilled bread, then the sauerkraut, then you'd squeeze on either mustard, thousand or Russian dressing and then top with the other piece of bread.