Sorry Natasha - I'm a little confused now. Is the drain outdoor or inside the property? If outside, and you are renting, report it to your landlord. If you own the premises yourself, look for an outside manhole cover and lift it. You will soon know if it cover a blocked sewer!!! If so, unfortunately you will have to seek professional help as caustic soda is absolutely no good in cases like that. If the sewer is blocked, that could account for the smell. Does the water in the loo run away OK when you flush? If it fills up and then drains slowly, that indicates a blockage.
If it is any of the above, caustic soda won't work. It may need the attention of professionals.