Performed visual inspection of drains for kitchen sink as well as upstairs bathroom sink to try and determine cause of smell. After inspection I believe smell is coming from organic material built up inside of tubular drains, strainers and drain assembly for sinks. Removed some build up in upstairs sink to try and aid in removal of the smell. Explained to customer we recommend replacing of drain assembly and tubular drains for upstairs sink and replacement of strainers, dishwasher hose and tubular drains for kitchen sink to try and stop the odors. Explained to customer that it is a process of elimination and this is the first step in trying to determine the cause of odor