Monitoring and cleaning drainage lines made from reinforced concrete slot units is easy, the maintenance costs are low. The drainage lines are easy to access through the openings in drainage manholes and cleaning pipes. In general, deposits can be removed by water using a high-pressure cleaner (jetting) through the slot. However, if necessary, flushing hoses of flushing tankers or jetting equipment can be fed into the slots from the manholes and cleaning pipes.