Kitchen sink airlock

[phil76]

Hi all. Just wanted to ask for some help as I'm stumped on this one...

So thought kitchen sink was blocked. Its new build and only moved in about 2 months ago... So I checked pipes under sink and all clear... Then ran a hose down the waste pipe under sink and checked to see it was coming out sewer. All fine. Ran water through all white pipework before connection to final downward grey wastepipe and it flows no problem. Connect white pipes to grey waste and hit problem. Really slow drainage again (i mean half hour to empty sink slow)

So after hours of banging my head of wall. I cut half inch of grey waste pipe so it was running level after u-bend into waste and not slightly uphill as previously. Also noticed that after u-bend on final straight stretch into waste the water level very low (using torch behind pipe), no matter how full sink.

So drilled a small hole in the straight section to grey waste and p****ssst, air flying out... and sink draining better... If I block hole again it airlocks. No idea why.
Can anyone help, as I don't think drilling holes in pipework should be the answer.. Also Sewers all look clear, but some toilet niceties are lying a little higher, due to heavy rain I think.

Have stuck a crude diagram on to help

MAny thanks

 

[stevetheplumber]

got to be blocked somewhere

 

[phil76]

I thought so too... But where? hose flows out waste into sewers no problem... pipework undersink is clear too, as tested... Sewers are clear...

 

[lame plumber]

could be 4" soil pipe doesnt have adequate vent on system, get onto builders

 

[zeebeedee]

Is the waste straight? If it dips then rises this could create a second trap and cause an airlock.

 

[snowhead]

Also Sewers all look clear, but some toilet niceties are lying a little higher, due to heavy rain I think.

Rain shouldn't affect any levels in the foul drain/sinks/toilets.
You shouldn't need any holes to force the drain to run.
Pipework out of level may cause a slight problem, but not enough for water to take 1/2 hr to drain.

You have a partial (almost but not quite complete) blockage.

It's between the sink and first inspection chamber.

 

[phil76]

Heres a pic.

 

[PlumbBobBob]

the very bottom of the white trap looks odd to me, strange angle on bend. there could be a restriction there.

 

[phil76]

the very bottom of the white trap looks odd to me, strange angle on bend. there could be a restriction there.

Maybe, but when i run the water through before connecting to grey waste, it flows perfectly. All it has to do from there is flow horizontal and down?

 

[Keefy]

Very odd looking trap. Does it create any noise such as a gurgling or slurping sound when you let a full sink go?

And is there any or much of a trap seal left when it's finished? Just that that vertical pipe just after the trap looks like it has the potential to create a vacuum.

 

[zzzjim]

Still sounds like a blockage further down drain,
as you pour water down grey pipe level rises pushing (Foul) air back out.

Hence why it works with hole (and eventually STINK)

 

[phil76]

Yes it does make odd noises, like a tap is dripping on sink and it isn't... and gurgling etc

Does anyone know --- kind of trap it is? its restricting flow and vacuum is created.. And yes vacuum seal was warped today. I had to refit it.

Is this dodgy plumbing? Or why else would plumber fit this? Also in house had broken seal on hot water in utilty and bathroom. And its newbuild, occupied for 2 months...

Many thanks for your help

 

[REDSAW]

'there may be trouble ahead'
run a hose for 1/2 hour

 

[phil76]

Still sounds like a blockage further down drain,
as you pour water down grey pipe level rises pushing (Foul) air back out.

Hence why it works with hole (and eventually STINK)

Sry no stink or level rising when I place hose in waste. When I put hose in waste it flows away and I can watch it in sewers...

 

[Rob Sale]

Try a different style of trap.

 

[zzzjim]

With hose in place down grey pipe,air can escape.

A bit of wet rag sealing round hose,
would give clues that air is squeezing past
(as pipe work is filling building pressure to get past constriction)

(Don't over-do seal Not pressure cleaning
--Like Blowing joints apart-Wet-n-Dry-On-Blow.!)