We have septic tank. Ranch style house.
Have tried every chemical. Have snaked plastic kitchen pipes. Flushing toilet in bathroom to the left of kitchen and running water in the bathroom sinks backs up the kitchen drain but tub is not affected . Second bathroom not affecting kitchen drain. Water filter connected to sink and no problem getting filtered water. Cleaned once the hose to where filtered water comes out. Possible plugged again?
Where is the clog? Why should flushing the toilet backup in the kitchen sink? Water eventually goes down but running the water afterward slows the water going down. Water coming up in not sewage.It is the water in the kitchen pipes. I used a plunger once in one bathroom sink and in the kitchen. Could I have made the clog worse?
Thanks

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Have tried every chemical.

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As a repair plumber I have never recommended using harsh chemicals. In your drainage system. Besides they only seem to work in TV commercials and when you try to remove the water you could burn your hands or damage your eyes.
You have a blockage downstream from the kitchen sink. This clog must be snaked from the kitchen roof vent. Put out enough snake to reach the base and 20 feet more. Flush wit a sink full of hot water. Good luck, Tom