What is this nipple sticking into a floor drain?

[Mikeygstl]

Residential home in the midwest, built in the early 60's There is what appears to be a pipe nipple sticking into the 4" floor drain pipe about 6" above the water level for the P trap, angled down at 35 degrees and only protruding maybe 5/8", but still beneath the concrete floor. Still trying to figure out how to get a pic of it on here, but was hoping someone had an idea from my awesome ascii art. the nipple appears at the + sign.

______________    ______________
              +  |
 ________     |  |
 ______  \ __/  /
       \_______/

 

[Reach4]

Trap primer?
Drain from humidifier?
Drain from AC?
Drain from softener?

 

[Sponsor]

 

[Mikeygstl]

I thought a drain at first, but it's only 1/2" pipe, and all of those that could/maybe have used it as a drain are above grade.

 

[hj]

It is probably someone's attempt at a "trap primer" inlet.

 

[Mikeygstl]

Hmmm - if a trap primer, any idea where the source of the water would come from? I've traced all the supply lines, but was guessing if it was from one of those it would need an air gap or backflow prevention of some kind. The direction the nipple comes from seems to point in the direction the line would be heading under the slab.

This is all out of curiosity, as I haven't seen anything like this in other homes I've looked at.

 

[Reach4]

Hmmm - if a trap primer, any idea where the source of the water would come from? I've traced all the supply lines, but was guessing if it was from one of those it would need an air gap or backflow prevention of some kind. The direction the nipple comes from seems to point in the direction the line would be heading under the slab.

Air gaps were not very common in the 60s houses.

 

[WorthFlorida]

Any sinks near by. For commercial environments a trap primer is feed from a sink drain tail piece. Generally you'll see it in bathrooms with floor drains. If your floor drain is is in a basement, look around the washing machine. The trap primer can also be from a water supply line. Doubtful for a home. It is possible that when the home was built, the plumber may only had this type of floor drain in his truck and the primer may not be connected to anything.