Option No. 4. The most difficult type of drainage.
At first, the sand of about 10 centimeters is poured at the bottom of the trench and is tamped. It will serve as a water filter and a pillow of the entire system. Then geots are laid, along the top of which gravel five to ten centimeters is filled up and a drainage pipe is laid in a special geotxed winding. Then a gravel is filled on top of the pipe that is turned into the same geothkani. Further, as well as from below, there is a layer of sand to cough centimeters and the drainage system is ready. The main advantage of this option is the presence of a double layer of sand that is a filter. The gravel itself is protected from the hit of small polluting particles by geothkani and the pipe itself is protected by it. These design features allow such an option not to lose their functions for a very long time, firms for the production of plastic pipes give a guarantee for more than fifty years, and the winding of gravel will extend the service life of the drainage of still fifteen.