The reason for the smell coming up from the bathroom drain is that the water is not used for a few days. The smell will go away as soon as the water is used again.

When the sink and toilet drain are clogged (especially if there is any substance are put in it ex: hair, etc.) You can use the unclogging chemicals which are sold from the supermarkets nearby and will be able to deodorize and clean the drain within 30 minutes.