All the work of the home local sewage system is based on the hard work of living bacteria, so the system does not like aggressive chemistry.
How the water seal is made and positioned, the levels and other issues of creating a sewer for the shower are chosen.
For the washbasin (sink), a folding bottle siphon is often used as a universal solution for connecting all plumbing fixtures to the sewer. Consider why it is used, how it is serviced, and how it can be replaced.
The smell from the sewer is not harmless. The air escaping from the sewers carries a large number of pathogenic bacteria.