By making an external sewage installation, the pipes are placed in the trench in this way, so that they have an equal decline 2-3 cm on 1 running m of the pipe ; towards the sump. The position of these pipes on the drainage layer will be easy to measure with a measuring tape, if earlier a string is drawn horizontally over the excavation. According to him, the necessary inheritance will be determined. In turn, the very horizontal position of the string can be very accurately determined with a water hose drawn along the entire length of the trench..