Old cabin... bathroom toilet bubbles when bath or kitchen sink are draining ? I wonder why?

Hi Marke1952:

If you are on a septic tank when was the last time the tank was pumped?

Bubbles usually indicate back pressure caused by a partial blockage downstream from the toilet. Rent a medium electric snake machine (Pic.#1) and snake the drain line from the roof vent or lift the toilet and snake drain from there. You may also want to purchase a pair of leather gloves and a pair of safety glasses... ;)

You may be able to confirm pipe is partially blocked by removing the main drain cleanout cover (just where sewer enters home) and then flooding the pipe with water so you can see if you hear any bubbling action at the cleanout. If there is bubbling noises then you would be best to snake the drain from the main drain cleanout itself, but in this case you would rent a LARGE snake machine (see pic. #2)... again, flood the pipes so you will know when you hit the blockage with snake.

If no issues at the main drain cleanout then back to the roof or the toilet if bubbling up in bathroom.

Let me know if you want to discuss in more detail...

MARK