And one more DWV 3D to examine and critique, please.

[3D Artist]

This is a half-bath. The question is whether the W.C. is properly vented. I drew a 3x3x2 sanitary tee to vent the 2" straight up through a wall.

As can be seen, I piped the lav drain so as to come into the 3" drain downhill from the W.C.

And how about this? I drew a sanitary tee for the joint where the lav drain will connect. Is this OK or do we need to use a combo wye and tee for this (very common) connection at a lav drain?

 

[wwhitney]

The sanitary tee does only one thing: it lets a drain turn from horizontal to downward while simultaneously allowing the vent to be taken off upwards. [And it's the only fitting that can do that.] That's it, it's not used anywhere else. [OK, you can also use it to join two dry vents above the their flood rim levels in lieu of a vent tee.]

So your 1-1/2" lavatory trap arm has to use a sanitary tee as shown. And you can't use a sanitary on its back as you've drawn, that should be a combo.

As can be seen, I piped the lav drain so as to come into the 3" drain downhill from the W.C.

As drawn, both your fixtures are individually vented. So there's no need for the above, you could bring the 1-1/2" lavatory drain into a 3" drain all in the same plane (use a 3" combo with a 3" x 1-1/2" bushing in the straight inlet). Also, I believe you are under the IPC, in which case you could vent the toilet with only a 1-1/2" vent (unless there's an aggregate vent requirement in the IPC that you need to meet, not sure about that).

Alternatively, you could wet vent the WC and have just one vent. In which case you'd have to join the lavatory drain to the WC as mentioned just above. Under the UPC, the lavatory drain and vent would have to be 2", but under the IPC it maybe OK to use 1-1/2", not sure.

Cheers, Wayne

 

[Sponsor]

 

[3D Artist]

Thank you, Wayne. I changed out the 3x3x2 sanitary tee I had laying on its back to accomplish the toilet vent, with a 3x3x2 combo reducing wye with 1/8 bend.

Not finding anything with appropriate hub sizes in a fitting with side inlet, I let the lav drain go as I had it.

But for future, is that legit, to pipe a drain straight into the side of a wye used this way? I thought all drains had to sweep and curve, not do just straight-in terminations.

 

[wwhitney]

The sanitary tee does only one thing: it lets a drain turn from horizontal to downward while simultaneously allowing the vent to be taken off upwards. [And it's the only fitting that can do that.] That's it, it's not used anywhere else.

OK, that's not quite right. That's the only place where you need to use a sanitary tee, but you can use it elsewhere. A better description:

The sanitary tee, when one of the connections is a drain, is only used with the straight path vertical, and the side inlet horizontal. In that configuration the side inlet is a drain, the bottom inlet is a drain, and the top inlet can be a vent or a drain. If the top inlet is a drain, both drains coming in had better be already vented, and a combo could be used instead of a sanitary tee.

Cheers, Wayne

 

[wwhitney]

Not finding anything with appropriate hub sizes in a fitting with side inlet, I let the lav drain go as I had it.

If you want to bring the lavatory drain into the 3" line at the location where you have the long turn 90, you can use a 3" combo:

https://www.homedepot.com/p/3-in-ABS-DWV-Hub-Long-Sweep-Sanitary-Tee-C5812LHD3/100342451

And then to bring the 1-1/2" lavatory drain into the inlet use one of these:

https://www.homedepot.com/p/3-in-x-1-1-2-in-ABS-DWV-Spig-x-Hub-Flush-Bushing-C58012FHD3112/100347343

It take a 3" hub on any fitting and turns it into a 1-1/2" hub. My examples are ABS, but the same fittings are available in PVC.

But for future, is that legit, to pipe a drain straight into the side of a wye used this way? I thought all drains had to sweep and curve, not do just straight-in terminations.

I don't quite follow the question. The way you've drawn the 1-1/2" lavatory drain joining the 3" drain is fine. [That's called an "upright wye" where you use a wye and a 45 to given two parallel inlets.] But joining them as above would be simpler and avoid a few fittings.

Cheers, Wayne

 

[Terry]

I would consider replacing the 3x2 samtee with a combo and using a 2x1.5 santee above that to arm over to pick up the lav.
Less drilling through floor joists that way and less pipe and fittings.

In my codes they don't allow santees on the horizontal like that.

 

[3D Artist]

Thanks, Terry! That lav that will now drain by running horizontally (sloped of course) through the wall over to the 2" stack, I can see how that eliminates taking it into the floor, but at the lav where the trap arm goes, is that a simple flatwise 1-1/2" ell?

In other words, is the lav vented by when it hits that 2" stack?