Using a household bathtub for film or print development is generally not recommended.

From a safety standpoint, black-and-white developers such as Rodinal are not usually considered extremely hazardous when handled properly, but they are still darkroom chemicals and should not be treated as something you want in contact with skin during later bathing. Even if the risk is low, residue in seams, drain areas, or hard-to-clean spots is an unnecessary concern.

Practically, a bathtub is also a poor processing vessel. It can stain over time, is awkward to clean thoroughly, and its shape is inefficient for consistent development. You would also need similarly large volumes for stop bath, fixer, and washing, which makes the whole workflow cumbersome unless you have multiple large containers.

No common developer is especially suited to direct bathtub use. A much better approach is to develop film in tanks and reels, and prints in trays or other dedicated darkroom containers. That uses less chemistry, is easier to control, and keeps bathroom fixtures free of chemical contamination and staining.