Will the river sand used for all the backfill in the bathroom sink?

The backfill of the bathroom is generally made of construction waste, as long as the surface slope is done well: no water, no leakage, it is fine.

No problem, everyone decorates like this.

No, because of the dual reasons of load-bearing and waterproofing! It should be backfilled with carbon slag! >>>More

Whether it will go down depends on what material you backfill and whether it is dense, and it depends on how well you do the ground surface, which has little to do with the brick lattice.

It's a two-person world, it's nothing, but if you live with your family, it is recommended not to use a glass door, which will be more inconvenient at some times.