What the City asks you to do when a drain backs up
Vaughan publishes an order of operations for a backed-up drain, and it is worth following.
Call a licensed plumber first. If you call the City first you pay a deposit for its investigation, and that money only comes back if the blockage turns out to be on City property. Before the lateral is opened, the plumber calls Ontario One Call for a sewer safety inspection, which costs the homeowner nothing.
That check exists because gas lines have been directionally drilled straight through sewer laterals. Responsibility splits at the curb box: house to curb box is yours, curb box to the main sewer is the City's. A camera run settles which side you are on before anyone quotes a dig.