The photo at right shows a floor drain as viewed from the side.
Old floor drain no trap.
The shaded portion shows the trap where water will always sit which prevents sewer gas from coming in.
Many older houses in minneapolis and saint paul have an old style of plumbing trap called a drum trap which is no longer allowed in minnesota except in special circumstances.
The main problem.
As water drains down the steep slope at the wye it can create a siphon effect such that water will be sucked out of the trap.
Many basement floor drains tie directly to the home s sewer system but in some communities local building codes require floor drains to run to a sump pit where a pump lifts the water to the exterior surface of the house.
Basement floor drains don t get a lot of attention until the sewer backs up or the basement smells like an outhouse.
Water in any trap under unused drains will eventually evaporate.
Connecting a trap to a vertical drain with a wye fitting and a 45 degree elbow seems like a good idea.
And the empty trap will allow sewer gas to flow into your home.
Solve that problem just by dumping a pitcherful of water into the drain to restore the trap water.
The drain pipe dips down in a u that is always filled with water whether flowing or still.
Floor drains are most often installed during original construction often in the utility area to drain away excess water in the basement.
You have a water trap under a floor drain laundry tub or wash basin that has dried out from lack of use.
Floor drains are no exception.
The drain trap is an important part of the floor drain.
The water filled trap prevents noxious sewer gases from backing up into the home.
In the short term try 5 10 bleach solution in water not just water.
A cup of bleach to a gallon of water 1 15 or about 6 7 it may be a floor drain to soakaway rather than connected to septic sewer but those can still get quite nasty especially if something crawls down there and dies.
