Here in Brazil almost all shower and floor drains are made using a device that translate as "siphoned box" and work as a trap collecting water from the sink, tub and shower.

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Is that any better (or worse) than a P-Trap?

EDIT: One advantage of this system, is that rings or earrings that get collect usually stays at the bottom of this device, which makes it easy to retrieve it. Also, is provides a easy access to another inspection point in the plumbing.

BTW: How prevalent are floor drain in bathrooms and laundry areas? In Brazil every laudryroom have a drain and some bathrooms have another drain besides the one in the shower. I heard that in Europe and US that is very rare.

  • I know these are common worldwide. I also know that they are not to code in Canada. But I don't know why. – Chris Cudmore Dec 11 '12 at 18:45

This is what is called a drum or barrel trap in North America. They used to be common many years ago. Then P-traps became available and were found to be preferable, leading to the banning of drum traps in model plumbing codes.

Unfortunately, I'm not privy to the reasons they were banned. Some disadvantages I see is they retain a relatively large amount of wastewater. In theory, some small portion could remain in the trap for quite a long time, possibly allowing mold, bacteria and other undesirable things to grow in there. P-traps, by nature, have more of a first in, first out sort of flow, minimizing the chance of old wastewater staying around. In the case of the shower and floor drains, the wastewater is in very close proximity to the drain grate. It makes it easy for occupants to come in contact with the wastewater, which would generally be considered an unsanitary event and thus frowned upon.

Floor drains in residential bathrooms are quite rare in the Northern and Western hemispheres, except where the floor drain also serves as a shower drain. I've seen such a configuration in mostly tropical and sub-tropical countries. Floor drains in commercial restrooms are so common, they might be required. I'm too lazy to check right now.

Floor drains in residential laundry rooms, while perhaps not common, are certainly seen often enough. Still, they are not required, so many laundries have none.

  • In Brazil I never actually saw P traps being used on showers, just on sinks. I found this plenaweb.com/gerar_imagem_prod_zoom.php?nm_imagem=/projects/… at a manufacturer, it is advertised for sinks, would it work for showers and tubs? – Luiz Borges Dec 12 '12 at 0:59
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    Just as another perspectice, a bathroom or laundry in Australia without a floor drain is very unusual. I think it may even be mandatory in new construction. – staticsan Dec 12 '12 at 2:19
  • Whenever I see the rare US residential bathroom with a floor drain I imagine cleaning the bathroom with a hose, and I smile to myself. – mac Dec 12 '12 at 4:15
  • @staticsan Yes it is mandatory in bathrooms and laundry's in AU, unless the floor slopes directly to an external door (fairly uncommon in a bathroom) but a dry floor waste can also be used, although it is an outdated way of doing things. But our floor drain are different to the one shown here as this looks like it could cause some serious blockages over time, ours have a minimum one size larger outlet than the largest inlet and goes on water load, also they are just an over sized s/p-trap – UNECS Dec 12 '12 at 5:21
  • @ Luiz: That P trap image looks interesting, it appears to be somewhat flexible, perhaps to ease clearing of blockages. Tubs and showers have different size requirements, if this product is available in the proper size, it could work for tubs and showers. Given that it is made from what appears to be lightweight material and is connected with hose clamps, I would be uncomfortable using it unless it was in a permanently accessible location. – bcworkz Dec 12 '12 at 23:47

So that trap works by collecting drain water from multiple sources through a single trap, and the water drains when the level in the reservoir rises above the bottom of the exit pipe on the right.

The name "siphon" implies that drain water exiting will create suction, pulling water out until it drops below the bottom of the exit pipe, about an inch deep from the bottom. I'm told, however, that this is not how it works, that the exit pipe must be properly vented, which means the water will fill up to just below the bottom of the exit pipe.

So my only concern would be that if you get a clog in the exit pipe, your sink water can end up in your shower. But that's true if your shower and sink connect below their traps anyway and get clogged after that connection.

  • Not true, level is always mantained at the exit (D2) which must be properly vented. The name "siphon" in this case is how we name traps (incorrectly I know). – Luiz Borges Dec 11 '12 at 19:11
  • Ok as long as D2 is vented, then suctioning it too low is not a concern. In which case, I see no problems with this kind of trap. – The Evil Greebo Dec 11 '12 at 19:32

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