Paint Thinner

Ya, apparently you're not supposed to pour it down the drain.

1. How adversely will that effect well water?
2. How long will that take?
3. Will that effect tank inhabitants?
4. Would an RO system remove petroleum distillate?

 

Paint thinner is a petroleum product and would contaminate groundwater as well as the surrounding soils.
Carbon will adsorb or remove most if not all of it since it is basically an organic solvent.

It will still have an adverse effect on the water in the well and the surrounding aquifer since only a fraction of a percent goes through the RO system or carbon. It takes years or decades to remove traces of contaminants from the water table. Ever drive by an old gas station that has been torn down and seen the monitoring and extraction wells that are drilled to treat the contaminated soils and groundwater. Contaminants like that are reported in and have health effects in the parts per billion not even parts per million.