I live in a townhouse with 3 other units and over the weekend my downstairs toilet backed up. The plumber came out today and found a diaper in the toilet. I do not have children that wear diapers but my next door neighbor does. Is there anyway that our plumbing is connected?

Depending on the age of the units you may have a back to back toilet or at least a common drain. Many newer fire codes do not allow cross penetration of a fire division wall. Was this a cloth diaper or a throw away one? At a minimum I would discuss this with your neighbor and see of they will help pay for the expense and politely ask them to stop diapers in the toilet.

Good answer ma, Sandra do you own or rent and is there a home owners association?