1.Rasam powder is easily available in markets.
2.If rasam powder is available then add a tbsp of rasam powder too while boiling.
2. I usually do not add hing/asafoetida/inguva in the tempering but it can be added if preferred.
3.Add water while boiling as required and do not keep the consistency of the rasam too thick. It is better if its consistency is maintained a bit watery.
4.Do not throw away the mashed tomatoes, instead they too can be blended into a fine paste and added to the tomato pulp while boiling.