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I've recently moved in to a new home. For a while the shower was draining really slow, as there was no access to the pipework (it's all tiled in), I ended up ripping the shower tray out in order to see what the problem was. The trap was badly clogged up with hair and other gunk, I cleaned it out and presumed that would sort the problem.

I put the base back in and ran water through it to test, but the problem still remains, it takes around a minute to drain a litre of water. I read that it may be because of a lack of fall on the pipe, so I raised the pipe dramatically, but it made absolutely no difference.

If I disconnect the trap, and run water through it from the tap, it's absolutely fine (it never fills, just runs straight out), similarly, if I pour water directly in to the waste pipe it drains away so quickly that I can't even see it filling up.

I'm a complete novice and have absolutely no idea what the problem could be. Any help would be greatly appreciated.

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    Sounds like a venting issue. Since you have it torn up, can you see where the vent is? Local code can vary, and the distance will depend on pipe size, but IIRC for 2" pipe the vent must connected be within 5' of the trap. – gregmac Nov 19 '14 at 18:55
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    There could also be a clog downstream of the trap. – Steven Nov 19 '14 at 20:14
  • @gregmac I think you're right. The waste pipe runs for a couple of metres and then disappears under the tiled floor, and I believe is connected to the bath's drainage (which is at least another 2 metres away). Problem is the bath is all tiled in as well with no access, so it's going to be a nightmare to get to it :( – billyonecan Nov 20 '14 at 10:27
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    5' is 2m, so even if there is a vent, it's still too far away (assuming the drain pipe is 2" .. you didn't say). This unfortunately means whoever did your plumbing didn't know what they were doing, so this may just be the start of problems. What to do next depends on the bathroom layout, and if you can find and access a vent stack. Your local codes may also allow use of an AAV (air admittance valve, aka 'cheater vent'), but layout will also dictate if that's even possible. Post some pictures and/or drawings of the layout (with dimensions relevant to plumbing) and someone might be able to help. – gregmac Nov 20 '14 at 15:42
  • Just to clarify vent distances. Codes are all different, where I'm from (Canada), the maximum length of a trap arm (the distance between the trap and the vent pipe) is determined by the slope on the trap arm, in that: the total fall of the trap arm cannot be greater than its inside diameter. The slope on 2" pipe is 1/50 so the maximum distance is 2.4m or 7' 10-1/2". – pdd Jul 19 '15 at 4:52
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The next step is to snake the drain with a plumbing snake:

A plumbing snake

Or to call a plumber.

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    or to re-vent the drain – Skaperen May 20 '15 at 11:12
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I mostly agree with gregmac. Though, the shower may be tied-in with the sink & using the sink trap. This isn't legal nor common, but would really be the only cause for your situation.

Just like you discovered with your test pouring, the pipe drains wonderfully without the shower trap. This is because the pipe isn't full, as it isn't with running a shower & the pipe will & does vent itself more than fine.

If this were a tub filling the drain line as it empties then & only then does venting play a or any role. So, check your plumbing...preferably from the ceiling below rather than ripping up the floor.

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