A check valve, or backwater valve, only works as long as it can seal. If a stick, paper, or any other object lodges in the opening, the backflow will still occur, although at a slower rate. The best solution is a combination check valve/ pump pit. In this system the check valve closes, but if any water infiltrates back, (or if you use water in the house), it rises into a pump chamber and the pump discharges it out into the flooded sewer system. This allow you to use water in the house, and also gives a positive backup to the check valve, as long as the power does not fail. If the power fails, then you would still have time to get a gasoline pump and suck the water from the pump chamber.
: We have recently had back flow from street drainage through our basement toilet whenever it rains exceptionally hard. The DEP has visited 5 toimes, flushed the drains, and said that we need a 24" drain pipe, not 12" running under the street. In the meantime, we have been told to install a check valve to stop the back flow. What is your opinion on check valves..do they work, are there any consequences from installing, etc. It's an expensive job so would like facts before doing. Thanks.