The “flapper” type check valve in main sewer lines is called a back water valve.
There is a rubber sleeve that does fit under the toilet much like a vacuum breaker sleeve installed under a flushometer like a Sloan Royal
As with most mechanical devices these too are prone to failure and up keep.
The proper location of a back water valve (check valve) is in front of the building house trap (Closest to the outlet of disposal from the building) and it has to be accessible.
If you use a rubber type of check the rodents will gnaw right through it.
Remember for every action there is a reaction.
Check valves (back water) make rodding difficult and thus they have to be able to be disassembled so the snake can pass right through it.
These device must be of an approved type that hang partially open to all free air movement to remove dangerous sewer gasses.
Best bet call the local utility in charge of the sewerage system and have them flush out this system with VERY hot water to remove any possible food source of these rodents.
UA Plumber class of 74
» This message has been edited by SylvanLMP on 30 January 2002