A modular toilet is disclosed comprising a toilet shell and a hydraulic core. The hydraulic core module is a separate unit from the toilet shell module and may be non-symmetrical with the internal and external form of the shell. The core module comprises a toilet bowl connected to a siphon drain comprising a weir. The drain may be a vertical loop drain. The toilet shell and the hydraulic core may comprise mutual sealing surfaces. The drain may comprise openings for connection to a toilet ventilation system.