the size of your domestic drain will be 4in, the the main shared sewer is 6 in and close enough then you could possibly push it into the main sewer providing there are no defects with the drainage, if you having blockage regularly then there will be defects so it maybe unlikely you would push the plunger past that. another factor is that the shared sewer may not change in diameter for 20-30m if you you will be pushing a long time.
i have removed plungers hundreds of times in the past but i used a CCTV camera to locate it and remove them, you may need to call a local drainage consultant to remove it, if you do call someone out let me know the area and i will let you know if i know anyone in that area that could help.
hope this helps you out feel free to ask any questions i will advise you as much as i can