How do you caulk a bathtub?

Grout is porus and degrades after time, the proper item to use would be caulking ( non porus and waterproof) also degrades, but can be replaced easily. Grout is preferred because it lasts longer, is pourous to a degree and will let water evaporate so that mold will not grow. Caulk is used for more temporary bonds such as between the sink and a painted wall. Grout, if installed properly can last you a lifetime.