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If I do away with the trap what is it going to hurt? Will something bad happen?

A friend had a problem with clogs. He took his out and has had no more problems. Can you tell me why that is?

Rob
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Michael Hodnett
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    They make P Traps with a removable cap to allow clean out. – Trout Aug 07 '16 at 14:05
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    I think you'll get a uniform, and resounding 'YES' from this one. Anyone that says otherwise should be first educated, and if they insist, be handed a candle. – Chris Aug 09 '16 at 20:45

5 Answers5

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The “P” trap (named after its shape, has nothing to do with urine) is there to prevent sewer gases from entering your home. It stays filled with water to form a barier.

You need it. Sewer gases are not good for you. In the right concentration they can even be explosive. Plus they smell really, really bad.

Everything that connects to the sewer needs such a barrier. Some things like toilets have the barrier built in. Sinks do not, so they need it in the pipe.

Your friend will eventually get a clog further down the pipe. This time he won't have a convenient and easy to take apart P trap for whatever crap he washes down the sink to get lodged in, so he will end up having to spend a lot more effort to remove the clog. Cleaning out the P trap (or just replacing it, if it was too gross to be worth saving a couple bucks) would have solved the clog problem just fine.

JDługosz
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Grant
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    Some old houses had just one huge trap on the cast-iron sewer pipe, a few feet before exiting the structure. (I've heard it called a "house trap".) I gather the idea of putting a small trap downstream of every plumbing fixture was an idea that came along later. If Michael Hodnett's friend has a house trap, he could easily believe the P-trap is worthless, because he'd have missed the #1 sign that something's wrong: the stench. He'd still have the other (invisible) problems the P-trap solves, of course... – Kevin J. Chase Aug 08 '16 at 01:57
  • My house has a trap on sinks which feed into a drainpipe with an air gap between it and the drain proper. The drains themselves have a U-bend below ground, before the sewer. So that's pretty thorough :-) I assume that having a trap makes sense almost regardless of where the pipe goes: it won't go anywhere that you actually want an air current back from, no matter how fresh. – Steve Jessop Aug 08 '16 at 14:35
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    Note that if the house has fixture traps you may consider removing the whole house trap. Whole house traps tend to corrode over time and leak sewage, and depending on the condition of the clean outs they may be hard to snake if they clog. I believe they are still required in New York, but are generally being removed elsewhere. – mfarver Aug 08 '16 at 15:50
  • @SteveJessop: Interesting! What era and region is your house? Is that typical construction of your neighborhood? – wallyk Aug 08 '16 at 16:37
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    @KevinJ.Chase Everyone I know who has one of those hates it. It makes any material that could clog have clogged one pipe instead clog up the whole house and flood the basement. One guy I know has at least two basement floods a year that have always been traced to the house trap. – Moshe Katz Aug 08 '16 at 17:42
  • @wallyuk: Oxford, UK, 1930s. I think the exterior drains are original, anyway our next-door neighbour has the same drains. The drains are to the side and back so I can't check whether everyone has them, but there are a lot of houses in the area built to similar plans (for workers at the Morris car plant in Cowley), so probably. I don't know whether the original sinks would have had their own traps: the ones we replaced weren't original anyway so maybe not. It certainly never occurred to us not to have traps just because the drains have them :-) – Steve Jessop Aug 08 '16 at 17:54
  • Anyway the house has a foul pipe completely separate from the sink pipes, feeding separately into the sewer. At some point I might roam the neighbourhood looking to see if everyone has the same foul pipes, and what arrangement people have made who've added toilets in attic conversions. – Steve Jessop Aug 08 '16 at 18:02
  • I used to live in an apartment with two bathrooms, both of which had showers but I only used the shower in one of them. After not using this shower for months I returned home one day to find the putrid scent of rotting increasingly filling my home — like old, dirty bins or decomposing meat. It started subtle but got worse and worse. Eventually figured this out and after running the shower for a little while it all went away. Lesson learned: don't neglect your plumbing. – Ryan Williams Aug 10 '16 at 10:08
  • @SteveJessop afaict the setup you describe with open pipes discharging wastewater into drains at ground level (often via a hopper and downpipe which may be shared with rainwater) is the norm in older UK properties. Newer properties tend to route the wastewater into the sewage stack instead. Houses that have been altered over the years will often have a mixture of the two systems. – Peter Green Aug 10 '16 at 15:46
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The p-trap creates a barrier between sewer gases and living space. It's foolish to think you can go without one.

Aloysius Defenestrate
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It's not clear from your question if he replaced the P-trap with another type of trap, or just removed it completely.

In the US, non-P-trap traps are not to code, because they are more likely to cause a siphon. And no trap is definitely not to code, for the reasons stated in the other answers (sewer gases)

BlueRaja - Danny Pflughoeft
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Never remove a P trap.

The purpose of the P trap is two-fold.

Firstly it prevents nasty smells from entering your home through the sink, as water sits in the bottom of the trap forming a barrier against movement of smelly air.

Secondly - and this is extremely important - it is designed to get blocked when people put things down the sink that they shouldn't.

Imagine if whatever it was that blocked it caused problems further down the sewage pipe, underground, or where it meets with the road. These could incur huge expenses to resolve.

So dealing with a blocked P trap is hardly worth thinking about when you consider the alternative.

Better still:

  • get a filter for the plug to stop solids such as hair going down at all
  • definitely don't put things like coffee grinds or other items that can build up over time into the sink
  • if you share the house with someone with long hair you are going to need to speak to them about it

If you rent, it's commonly accepted in most rental contracts that tenants are responsible for ensuring pipes remain clear. Expect a landlord to get pretty annoyed if you let pipes block regularly, as it costs him money to resolve.

hazymat
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    Hair is easily dealt with using caustic soda, as is grease. Just read the safety instructions first and follow them. If you're doing this frequently that suggest a greater problem, but every few months is reasonable. – Chris H Aug 08 '16 at 08:06
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The other reason to have a p-trap: Suppose someone drops a piece of jewelry down the drain. It happens. You'll definitely breathe a sigh of relief if you can recover a dropped ring or diamond earring from the p-trap rather than losing it forever or tearing apart your home's plumbing to try to recover it.

bearvarine
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