Step by Step ProjectsTips from the ProsAffordable Remodels
From the TOH Online article When Faucets Drip and Toilets Run, Fred asks:
"Everytime I use the upstairs crapper it shows up in my kitchen sink. Is this bad plumbing or my disturbed teenager? Why is this happening?"
A plumber would probably have a more indepth response, but I'd suspect 1 or more blocked plumbing vents - check every vent on the roof, make sure they are not blocked with anything.
If that's not the issue, suspect bad plumbing, but that should have shown up as an issue when the house was built.