I live in an apartment house. 189 families and 7 floors. I am in the 05 line,#205.
I have complained to the super who is #105 ground floor. My kitchen sink backs up and his sink backs up worse. He checked the apts in the line and he claims one apt 605 hides the washing machine apods he comes up. Catching the culprit is not working out.
My question is: Is there anything that could be put in the line which will redirect the suds back up? The super tells me there is nothing because the suds are light in weight.
Any ideas? Thank you.

Backups are caused by blocked lines. Has your super snaked out the drain line downstream from his sink?
"My question is: Is there anything that could be put in the line which will redirect the suds back up?"

No there is not. Your super was correct. Good luck, Tom