A modular toilet bowl assembly bowl assembly that allows adjustment of the relevant dimensions of the inlet of the outlet as well as the height of a toilet bowl without modifying the toilet bowl body. The toilet bowl includes a toilet bowl and upper drain pipe portion that are formed integrally as a single piece, a lower drain pipe portion that is formed separately from the toilet stool. The lower drain pipe portion may be formed of a series of parts having known dimensions so that by interior moving predetermined parts, the length or height of the toilet bowl can be adjusted.