In general, feeding rainwater directly into a septic tank is not advised. Septic tanks are made to handle effluent from showers, sinks, and other bathroom fixtures in the home.
The same kinds of toxins that are commonly present in residential wastewater are not found in rainwater, which is not regarded as a source of wastewater.
It might be conceivable in some circumstances to gather and use rainwater for irrigation or other non-potable uses. However, it’s crucial to make sure that rainwater is gathered and stored in a way that is secure and in accordance with local laws.
Instead of pouring rainwater into the septic tank directly, it may often be required to establish a separate rainwater collection system.
A professional engineer or a septic system expert should be consulted if you plan to use rainwater for irrigation or other uses. They can evaluate your home and assist you in choosing the best option in terms of price and functionality.