This plumbing work stinks.
Each plumbing fixture in a home connects to a drain/waste/vent (DWV) piping system that takes wastewater to the municipal sewer or a septic tank. Those sewers and septic tanks produce gases and foul odors that (unsurprisingly) we want to keep out of our homes. To do that, each fixture’s drain should have a trap that holds a small plug of water to block these gases. The sink in this photo lacks a trap, so sewer gases can enter the living space. Time to call a plumber.