Older Markham homes and newer subdivisions
Unionville and the older parts of Markham have mature trees and original sewer laterals. Roots get into clay pipe at the joints. The symptom is usually a slow main drain that gets worse after rain, because groundwater rises and the roots swell. A snake can punch through the roots. They grow back unless the damaged section is repaired or the line is jetted and then checked on camera.
Newer communities such as Cornell, Angus Glen, and Cachet tend to have plastic drains and newer water lines. The calls there are more often fixture failures, leaking supply lines under sinks, and basement bathrooms that were roughed in and then finished without a proper vent. A missing vent makes a toilet gurgle when the washing machine drains.
Markham winters also split pipes that run through unheated garages and exterior walls. If you lose water to one bathroom only, it may be a frozen line rather than a closed valve. Opening every tap and calling before you apply direct heat to the pipe keeps a frozen section from bursting while you are trying to thaw it.