Abstract: A drainage unit comprises a first drainage trough and a second drainage trough; said second drainage trough being located adjacent to said first drainage trough; said first drainage trough being configured to attach to a drain cover in order to allow fluid to flow into the first trough; said second trough comprising at least a wall which projects laterally from said first trough; said wall being suitable for accommodating a sub-floor level rail or frame of a door; a number of openings located between said first and second drainage troughs; whereby fluid flows from said second trough into said first trough through said openings. In preferred embodiments, the drainage unit provides an integral level door threshold solution.