Where should the type information be 238

Conceptually simple, but in practice...

That's the basic design here too (and almost the same names, though I generally see what you call a "swept tee" sold here as a "sanitary tee").

However, in a house of this age here, it's typical that people have added and relocated fixtures quite a bit over the years, so they're often quite far from the main stack. To prevent suction on branch lines from pulling the water out of the P-traps, you either have to have another vertical vent, or a vent pipe that reattaches to the main stack above the drain line, or (in some areas - they're not permitted everywhere, AFAIK) an AAV. An AAV is a little vertical stub coming up out of the swept tee with a diaphragm valve on top; it lets air when the drain is in use, but prevents sewer gas from escaping.

AAVs are really convenient for putting a sink in an island in the kitchen - no adjacent wall to run a vertical vent pipe, so prior to the introduction of AAVs (and in areas where they're not permitted) you had to come up from the tee, make a 180-degree bend (two 135 elbows and a 45), and run another vertical pipe back down through the bottom of the sink cabinet and the floor next to the drain pipe; that enters the stack above the drain and serves as the vent. Now you just stick an AAV on top of the tee in the sink cabinet.

Still simpler than those non-return valves you guys use in your toilets. Man, they're at lot harder to fix without tools than the ones over here. (I never seem to get a hotel room with a toilet that doesn't need *some* adjustment.)

4" seems to be more common in the US for the main stack, and either 3" or 2" for branches to sink drains. Closet (toilet) lines are still typically 4", I think.

Yep. Haven't had that in this house yet, though.

Anyway, during a good storm the pressure will change fast enough as the wind blows to make the water in the bowl surge up and down slightly but visibly - maybe a couple of centimeters from the normal line. It might be that wind shear across the top of the stack vent is sufficient to momentarily cause lower pressure in the stack than in the bathroom (which is not terribly well-ventilated), or the pressure differential might be the other way around.

Since this is an old, leaky house, we get a lot of pressure effects during storms - the flapper on the stove hood vent bangs, for example. Still, it's nothing compared to the way the suspended ceiling tiles would pop out of their frames during hurricanes, in the Mbuttachusetts house where I grew up.

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Let's say the conservative is the quiet green grin of the crocodile ... an' the liberal is the SNAP! -- Walt Kelly