I have had several letters recently about bad smells and even flies coming up out of basement floor drains and sump pump pits. One viewer was quoted hundreds of dollars to break up the entire basement and replace all the sewer lines.
The real problem is usually that the trap under the floor has dried out, allowing gasses back up the drain. Or in the case of a sump pump, you don't want to close it totally off because you want any water in the basement to be able to drain into the pit and get pumped out, but that terrible old standing water can get bad.
A drip valve
There is a common plumbing solution to dry traps that is a bit better than digging up all the pipes in the floor. You can install a special valve in a cold water line near-by that preferably goes to a clothes or dishwasher. When the machine uses it's solenoid valve to snap the water on and off, that jolts the system a bit, causing this valve to squirt a little bit of water into the floor drain, keeping it wet. They call this a drip line, drip valve or trap primer.
You do have to dig a little trench along the concrete to bury the pipe that takes that water to the drain. Many plumbing codes, like the City of Toronto, require drip lines to basement floor drains in new construction and it is up to individual inspectors as to whether they will accept the Dranjer as code compliant.
In Winnipeg there was a problem of Radon gas coming into houses through these dry traps, so someone came up with a whole series of ingenious little dry traps that insert into existing floor drains and even sump pump covers.
The most common one is shown here up-side-down so that you can see the little rubber ball that makes it work.
When in place, as you can see the water simply floats the ball up and when the water evaporates, the ball seals the trap tightly. This one is designed to go into the lid of a sump pump, so all the bad smells stay inside the pit.
This photo shows the same concept in a smaller form with a little floating ring. This can be put right into the floor drain under the grill.
As you can see, water flows through it, but when the water dries up, the ring closes off all gas movement. Even back pressure won't open them up.
For more information follow this link to the "Dranjer" web site.