Why does the tomb flow when it is used?

It's related to the timing of use.

The direction of grave sweeping is a very special geomantic layout, which requires not only specific geographical conditions, but also precise direction selection and careful construction, so it is called advanced geomantic layout. One of them is used immediately because it is related to the time of use.

The main principle of this layout is to choose the center of the mountain stream and build a long dike perpendicular to it to form a pond.