Sewer gas from garage floor drain

[Davej]

I have a floor drain in the center of my garage. Over the summer, we smelled sewer gas coming out of it, so I poured some water in there - I haven't really smelled sewer gas in there since. However, I keep noticing the water level dropping below this other pipe that intersects with the drain pipe. Can anyone tell me what I am looking at? See the attached pictures. That pipe that is perpendicular to the drain pipe is 20" down from my garage floor. I keep having to add water every couple weeks.

Perhaps pertinent info:

1) House was built in 1991
2) A plumber told me it just add water to it. Said it was tied into sanitary sewer so the water can get treated - storm sewers dump into lake erie and are not treated, so any garage chemicals/fluids would go straight into the lake.
3) My toilets drain very weak/slowly. I had a different plumber than #2 look at it - he blamed it on my 20yr old builder grade briggs toilets. He suggested replacing one and reevaluating. Replacement toilet (toto) arrived, will be installed after Thanksgiving. He inspected the vent stack on my roof and it was open - he had me flush a toilet while he was on the roof. I don't have any drain complaints with my sinks, tubs or showers.

 

[Reach4]

If you are not liking adding water every 2 weeks, you could use vegetable oil instead.

New toilet is a good idea.

 

[Sponsor]

 

[hj]

I am not sure what the photos are showing but a lateral pipe above the water line usually comes from some auxiliary drain connected to it. Some one may have wanted to sell you a toilet, because toilets do NOT "wear out", but can need servicing by a qualified plumber.

 

[Davej]

I am not sure what the photos are showing but a lateral pipe above the water line usually comes from some auxiliary drain connected to it.

If I pour a bucket of water into the floor drain, that lateral pipe that intersects it is below the water line for a couple weeks.

 

[hj]

If it were installed properly there would NOT be any room inside the trap for the pipe to be connected below the water level. As a side note, most areas do NOT want to treat "garage floor wastes" so the do not allow them to be connected to EITHER the storm sewer or the sanitary sewer. Commercial garages have to capture them and have a "haz mat" company dispose of them.