Adding a Trap to Existing Drain

I have a floor drain with no trap. I'd like it to have a trap - very much so.

Any obvious issues with this plan? Or shortcuts (some kind of drain with integrated trap?) Thanks.

I'll be the one to ask... how is that drain vented?

The drain vents to a stack in the wall maybe 10' away. The bottom of the existing drain is maybe 18". Pipe is 3" diameter. Right now air flows freely in and out of the drain (as shown by the green odor vapors.)

This was hashed out in a previous thread but my best guess is the plumbers thought it was for a utility sink when the foundation was poured, because there's no trap, drain, or slope in the floor... just an open pipe cut down to the concrete. But the A/C condensate uses this, so it's both necessary and obviously part of the original plans. Otherwise I'd just tape it shut.

I just want to know if the diagram (which I enjoyed making far too much) is reasonable.

(edit)

Essentially, will this work or do I need to dig down past the existing elbow and put in a P-trap. I suppose that's quite a bit less materials, too, just more digging.

Most plumbers would tell you to not use the s-trap but to go a little deeper and install a p-trap. Otherwise it looks fine to me if it is vented..

I would do it right and dig down far enough to put in the p-trap inline with the pipe...
If this is not in a high traffic area I would be tempted to put in a floor sink while the floor is open...
A 3" enameled cast iron floor sink with a brass grate for the top runs about $85 at the suppliers...

I'll do some checking on materials... but this is a zero-traffic area: it's actually under a false floor, so it doesn't even have to look good, which is great news for me. (I mean, there's no tile to redo or even concrete finishing to get perfect. It's "driveway-quality" concrete.)

Sounds like the P-trap is definitely the way to go... just didn't think of that initially.

pipe

That is not a drain, it is a cleanout that someone removed the cap/plug from. Probably to put the AC condensate drain into it, which is also unwise and possibly illegal.

Maybe, but this doesn't seem like a logical/convenient place for a cleanout... there's really no reason to have any plumbing on this side of the building except for this "drain" and associated vent. (Also, it's deeper than my diagram might imply: it's 18"-24" straight down before the elbow.) Restrooms, cleanout, utilities and main sanitary line are all clustered at the opposite end of the building.

It's also the only floor drain in the building, and since the cement floor is 12" below outside grade I'd assume the designs would call for one there. That and it's convenient for the under-floor A/C location. But good thinking; it wouldn't surprise me.

I may see about putting pressure on the contractor to at least fix this. There are lots of little things wrong or unfinished but the owner of the building didn't know to actually "inspect" the completed construction other than a casual walk-through before signing-off, so maybe I can plead with them since it was such a no-hassle close on what's really an expensive building for it's size.

I do commercial plumbing for a living and it is routine that we run underground mains throughout the site prior to the building going up as part of our "base build" contract that includes the skeleton of the plumbing system, public washrooms and roof draims etc...
Then as suites are rented/leased, the new tenants decide what should be changed in their area...
It is typical for us to put an end of line cleanout in the middle of a floor with no other plumbing nearby...
That allows us to tie into the main later downstream (or at the C/O) by cracking the slab and doing a bit of digging...
It also serves as a marker (visible) as to the location of the main for future reference...
We also routinely install unused water supplies, vents and wastes that go nowhere (they run up columns and branch off and are capped) as specified on the base build plans - these are designated for future use should they be required...