Trudging through sludge is a difficult task that requires a lot of effort and determination. The term 'SLOG' is often used to describe this type of activity, as it implies a slow and laborious process. It is usually used to describe a situation where one has to push through a difficult or unpleasant situation in order to reach a desired outcome. This could be anything from a long hike through a muddy terrain to a tedious job that requires a lot of hard work. In either case, trudging through sludge is an apt description of the effort required.