What is this ?

[Norm Peery]

I have never seen this before. No conventional trap present. Can anyone ID this?

Norm

[Rick Cantrell]

Bottle trap

[Norm Peery]

Thanks, Rick

[Joe Funderburk]

P3201.5 Prohibited trap designs. The following types of
traps are prohibited:
1. Bell traps.
2. Separate fixture traps with interior partitions, except
those lavatory traps made of plastic, stainless steel or
other corrosion-resistant material.
3. “S” traps.
4. Drum traps.
5. Trap designs with moving parts.
A trap is a simple U-shaped piping arrangement that
offers minimal resistance to flow. Certain traps or arrangements
are prohibited.

Code commentary: ...
Item 2 refers to separate fixture traps with interior
partitions, except those lavatory traps made of plastic,
stainless steel or other corrosion-resistant material.
Such lavatory traps are sometimes referred to as bottle
traps. This item refers to independent traps that are
not integral with the fixture. For example, water closet
traps are a form of partition trap, but because they are
part of the fixture they are not prohibited. Partition
traps are single-wall traps that rely on a single partition
to separate the house side of the trap from the sewer
side of the trap. Although they may be made of corrosion-
resistant material, they are still subject to corrosion
and can fail structurally. Because such failure
does not result in leakage, there will be no indication of
the lost trap seal.

[Joe Funderburk]

"P3201.1 Design of traps. Traps shall be of standard design,
shall have smooth uniform internal waterways, shall be
self-cleaning and shall not have interior partitions except
where integral with the fixture. Traps shall be constructed of
lead, cast iron, cast or drawn brass or approved plastic. Tubular
brass traps shall be not less than No. 20 gage (0.8 mm) thickness.
Solid connections, slip joints and couplings are permitted
to be used on the trap inlet, trap outlet, or within the trap seal.
Slip joints shall be accessible."

A bottle trap is not self-cleaning and is prohibited by the IRC and IPC in my opinion.

[Rick Cantrell]

After seeing several in new homes and remodels.
(Almost all pedestal sinks use a bottle trap, just about the only thing that will allow the close fit to the wall.)
Anyhow, I asked the AHJ, and was told they (AHJ) do not disallow the use of bottle traps.

[H.G. Watson, Sr.]

A bottle trap is not self-cleaning and is prohibited by the IRC and IPC in my opinion.

You do know what a lavatory is, right? (pictured).

The partition trap is allowed, it is servicable as well.

The outside cover finish appearance is no indication of what the material constituting the trap itself actually is INSIDE (most often plastic at the big box stores).

You first quoted what actually ALLOWS this within the ordered list as an exception to what is prohibited. Granted its a specific permissive listed as an exception ("except those") to a generalized prohibition...but the model code language you first quoted permits a separate-from-the-fixture (not integral to the fixture) partition trap for a lavatory.

You then quoted the commentary that further explained its (unammended) permissive use.

P3201.5 Prohibited trap designs. The following types of
traps are prohibited:

2. Separate fixture traps with interior partitions, except
those lavatory traps made of plastic, stainless steel or other corrosion-resistant material.

[Joe Funderburk]

The partition trap is allowed, it is servicable as well.

That's the problem as I see it. Service is not supposed to be required, as the code says it should be "self cleaning".

P.S. You misspelled serviceable.

[Jerry Peck]

(I added bold and italic to the quote below)

P3201.5 Prohibited trap designs. The following types of
traps are prohibited:
1. Bell traps.
2. Separate fixture traps with interior partitions, except
those lavatory traps made of plastic, stainless steel or
other corrosion-resistant material.
3. “S” traps.
4. Drum traps.
5. Trap designs with moving parts.
A trap is a simple U-shaped piping arrangement that
offers minimal resistance to flow. Certain traps or arrangements
are prohibited.

Code commentary: ...
Item 2 refers to separate fixture traps with interior
partitions, except those lavatory traps made of plastic,
stainless steel or other corrosion-resistant material.
Such lavatory traps are sometimes referred to as bottle
traps. This item refers to independent traps that are
not integral with the fixture. For example, water closet
traps are a form of partition trap, but because they are
part of the fixture they are not prohibited. Partition
traps are single-wall traps that rely on a single partition
to separate the house side of the trap from the sewer
side of the trap. Although they may be made of corrosion-
resistant material, they are still subject to corrosion
and can fail structurally. Because such failure
does not result in leakage, there will be no indication of
the lost trap seal.

Note that the code itself says not allowed ... except ... then the commentary explains that even those excepted by the code should not be allowed as they can fail with no visible signs of that failure as the failure is fully internal to the trap.