There are two reasons for this:
First, there is a crack in the back of the basin. After the basin is filled with water, the water enters the inner layer of the basin through the overflow hole. If there is a crack, it will leak. The treatment method is to fill the crack with porcelain mud.
Second, the fixed position of the lower water hole, the ceramic basin drain is not flat, the installation mat can not be tightly combined with the ceramic surface will leak water. The treatment method can be used to smooth the drain.
