When installing a bathroom sink, a pipe travels down from the sink to the wall. This pipe has a bend that is called the trap, and it is so named because its design is meant to prevent odors from traveling back up into the bathroom. One popular model in Europe tends to be the bottle trap, but what is it, and how does it compare to other sink-trap types?
The Bottle Trap
Sleek looking, the bottle trap is a style that emerged from Europe where compact bathrooms are common in many older buildings from the 19th century and beyond. The trap part occurs directly under the sink's drain hole where the main pipe connects. The bottle trap, where the curve is essentially housed inside a canister, gives the look of an upside-down bottle leading into the pipes.
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It's through piping bends and curves that some water remains behind to block odors and sewer gases that can reenter the bathroom. A common style is the P-trap, which is highly effective and common. The bottle trap essentially uses a P-trap-style bend created with an internal partition inside the bottle. However, this partition is welded in and can corrode, and there's no way to tell if it's failing from the outside.
The compacted shape of the bottle trap means the pipe is shorter and doesn't have to extend as far from the wall, making it perfect for narrow- or low-profile sinks and tiny basins. However, the potential for the interior divider in the trap to fail is why it's frequently not allowed to be installed according to building code. Even if the city allows it, condo or apartment policies may not, so be sure you can install a bottle trap before purchasing one.
If you look at a sink and its plumbing from the side, you may see that it extends straight from the wall and then dips down and curves back up, much like the letter "P." This is called a P-trap. That dip down and back up is basically the same waste-water travel pattern in use inside the bottle trap except the true P-trap does so with a full length of pipe.
For narrow sinks, a shallow-basin waste trap or a shallow P-trap will do the job for you. "Shallow" means it accomplishes the same thing but over a shorter distance or with a lower profile than a traditional P-trap might.
P-traps are highly effective and are easy to flush and clean, and they usually meet building codes.
Another common trap you might find at the home center is the S-trap, commonly used on kitchen sinks, but you should avoid these. Like the P-trap, if you look at the S-trap from the side, you'll see an "S" shape. It requires more space to install, but that's not why it has fallen out of favor or why many states have made the S-trap illegal.
The reason is that the construction allows for a possible siphoning situation that causes the water to get completely drained out so sewer gases emerge from the drain.
Many countries don't even have traps on their wastewater pipes, meaning bathrooms can often smell of sewage. It's not unsafe, and you won't get sick from sewer gases because they can't hurt you. It's just an unpleasant smell.
Even if a bottle trap's sales description calls it a P-trap, the building code may not see it that way. Be sure to investigate your local code before choosing the style of trap that is required in your area. Just because the home center sells it doesn't mean it's legal.