My bathtub drain became very slow a week ago. My toilet next to it flushed slower too. When I flushed the toilet, from the bathtub drain it would come up with some bubbles and water like a little vocano. Ocasionally the sink drain next to the toilet, further away from the bathtub would bring bubbles and water in the toilet and the bathtub too. I tried snake the toilet. The snake was 7 meters long. It came out all clean from the toilet. I used about 1 kg Mr. Magic caustic soda and baking soda mixture with white vineger in the bathtub, toiet and sink. I poured hot water into the bathtub and toilet. It hasn't got any better. Any idea why and what I should do next? Thanks. The picture I attached I found online. It's very similiar to my bathroom setup.