Please check the following.
There is a place to collect water called traps in the drainage area around the water, and it has a function to prevent invasion of odors and pests from the sewer pipe.
If the water is not used for a long time due to absence, the water in the drain trap will evaporate and the odor will go up.
If there is no improvement after trying the above, please let us know via the "Contact Us" form,
Or Please contact the service center.