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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?

  • 1
    They make P Traps with a removable cap to allow clean out. – Trout Aug 7 '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 9 '16 at 20:45
88

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.

  • 8
    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 8 '16 at 1:57
  • 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 8 '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 8 '16 at 15:50
  • @SteveJessop: Interesting! What era and region is your house? Is that typical construction of your neighborhood? – wallyk Aug 8 '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 8 '16 at 17:42
13

The p-trap creates a barrier between sewer gases and living space. It's foolish to think you can go without one.

10

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)

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    I am pretty sure that was not an innocent mistake. (The wrong title) – Shadow Wizard Aug 7 '16 at 21:34
  • @ShadowWizard: I was referring to "He took his [p-trap] out". He had to have replaced it with something, but it's not clear if that's another trap or a plain elbow pipe – BlueRaja - Danny Pflughoeft Aug 8 '16 at 19:32
  • I meant using the word "pee" instead of "P". – Shadow Wizard Aug 8 '16 at 19:50
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    @ShadowWizard: I understand that, but I don't understand why you commented on my answer because I did not reference that at all. – BlueRaja - Danny Pflughoeft Aug 8 '16 at 20:42
  • In older houses I've seen some interesting-looking trap arrangements that appeared to be designed to avoid siphons (for pipes exiting via the floor, with no riser proceeding up from the trap). Did such things not work acceptably, or why have they been so universally replaced with P-traps and risers? – supercat Aug 8 '16 at 23:05
10

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.

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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 8 '16 at 8:06
6

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.

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