We recently bought a house, being first time home buyers we don't have much knowledge. After closing and moving-in, We found the bathroom in the basement was constructed totally illegally. The hot water faucet is on the right side while cool one on the left. Most serious thing is that there is no plumbing vent for that bathroom, it often causes the sewer backup, and the gases inside the sewer pipe leak into the basement, making the basement smells bad. However the home inspector haven't found these issues during the final home inspection. We are wondering if the seller or home inspector should take any legal responsibility on this issue?