The house is one year old, the bidet has a terrible smell when it rains, also toilets are constantly clogged, could both problems be related? maybe main cleanout is clogged? Vent pipe problems?
Need more info: Municipal waste or septic? Were the waste pipes in the basement visible? Did you get on the roof to look at the vents?
I haven’t been to the home yet, it is slab construction, I think it is septic most houses in this area are.
Sounds like the tank might be filling due to heavy rain. An indication of a bad installation. If you don’t inspect septics, you might want to recommend that the tank be cleaned and inspected while you are there. Could also be a venting issue. Look for AAV’s that may be installed or vents that are capped / blocked.