Should I open a cap to check whether the sewer is full?
No. A backed-up opening can release wastewater. Describe the visible fitting and symptoms when arranging service.
Detroit, Michigan · Drain and sewer services
A practical guide for Detroit homeowners.
A cleanout is an access fitting for inspection or cleaning. Its position depends on the building and pipe route; an ordinary drain grate is not automatically a sewer cleanout.

Look for a capped fitting near the base of a soil stack or along a known drain route. Note what is visible without opening it. A threaded plug may be corroded, and a backed-up line can release wastewater if the cap is loosened.
DWSD explains that many Detroit sewer connections run toward a rear alley or former alley. Existing property records or a previous camera location can help establish whether that pattern applies to the house. Do not assume every sewer runs toward the front street.
A previous inspection report, repair receipt or location photograph may identify access that is now concealed by storage, landscaping or a floor finish. Keep the access point distinguishable from water, gas and other utility fittings.
If no suitable opening is available, the technician should explain alternative access and any fixture removal or fitting work. For proposed excavation, utility locating and the applicable permissions belong in the plan before ground is disturbed.
No. A backed-up opening can release wastewater. Describe the visible fitting and symptoms when arranging service.
Not always. Fixture removal, bends and pipe condition affect access. A suitable cleanout is assessed first.
Main Line Drain Cleaning in Detroit — Investigate the shared drain serving several fixtures.
Call with the address, affected fixtures and any previous inspection details. The phone line is available 24/7; confirm the current service window and proposed scope on the call.