Full Bathtubs – It is recommended to caulk the bathtub when it is at last 3/4 filled with water. The water weight will produce strains over the surface creating the largest possible joints between the wall and the bathtub. The water-weight will allow the tub to set at it’s lowest point relative to the walls surrounding it while the silicone dries for 24 hours. Otherwise the tub will sag when you get in and pull on the seam causing possible long-term cracking and breaking.
Just another expert idea from Guy Calor, the Caulk King and CaulkWarmer!