I'm not a plumber, but if there is a smell coming up it usually is not because it is blocked... usually means no water in the trap (elbow thingy that has a water-lock to prevent gas / smells travelling up into the house).
Typically only reason this happens at the bath is because a fitting is lose or cracked which allows the water out from the elbow.
Two issues: 1 the smell you are getting and, 2 the water is going somewhere and could be leaking under bath with possible unwanted consequences.
Suggest you remove the access panel (or side panel which ever gives you access to the drain side with the water lock elbow) and verify it is not cracked, split, rubber not seated, tight enough, no leakage etc... replacement elbow is cheap enough and easy to replace... water damage can add up very quickly so would check sooner rather than later.
Good luck.