P trap vs S trap

[thunderhead]

I have been reading on the internet and now I am more confused than ever. Can someone explain in layman's terms what makes it one or the other? Is this picture a P or an S trap? Also, in this video I think the guy is getting confused but I think he was going from an S to a P. I just don't understand the difference. Thanks https://www.youtube.com/watch?v=y9NBdZcH3nE

 

[Sylvan]

P trap NOT vented so some may consider it a S trap as it will self siphon

 

[Sponsor]

 

[Terry]

I would call that p-trap an S trap. No venting there. It will siphon. Yep.

That video you posted is so wrong. Done by a handyman that has no plumbing knowledge.

 

[thunderhead]

The drain goes into the basement, runs about 2' and then a vent going through the roof. Is that not venting properly?

 

[Terry]

Not even close to being right.

What we normally do.

 

[Jadnashua]

For a vent to work, it MUST exist BEFORE the outlet from the trap turns downwards, and it must be within a specified distance from the trap. The drain lines should slope a minimum of 1/4" per foot, so say it was a 2" pipe, at 1/4" per foot, there would potentially not be an air path if the distance to the vent was more than 8' and the pipe got full, but to account for other variations, at least in one code version, on a 2" pipe, that vent must occur within 5'. If you can look at the stuff from the side, and trace an S-shaped one prior to it being vented, you have an S-trap.

In your picture, IF they're allowed, the easiest way to vent it would be to add an air admittance valve (AAV).

 

[Sylvan]

Rule of thumb

A fixture should be within 2 feet of a trap and a trap should be no more the 2 feet from a vent