Weird gurgling sound coming from kitchen tap

[Adsibob]

After and during some heavy rainfall our kitchen tap will make an intermittent gurgling sound. It lasts for anything between 1 and 4 seconds then stops for about 3 to 5 minutes then happens again. In case it’s relevant this is the type of trap we have under the kitchen sink:

 

There is also a flexible pipe bringing the dishwasher waste water into this, although the angle of the photo hides it - I don’t think it’s relevant though, as the dishwasher wasn’t running at the time of the noise.

 

The only explanation I can think of is that as our sewer fills up with rainwater it changes the amount of airspace in the drainage system and that causes pressure changes which affect the trap??? Not a very convincing explanation but it’s all I’ve got.

 

Any ideas?

 

It’s not bad enough or frequent enough to really bother me enough to do anything about it, other than to want to know why it’s happening.

[dpmiller]

do you have a vent stack?

[Adsibob]

9 minutes ago, dpmiller said:

do you have a vent stack?

Not sure. I don't think so. Where would it be if I did have one? As part of our renovation and extensions our house was completely replumbed recently, to relatively modern standards, but the plumber did cut a couple of corners. Should he have installed one? 

[Radian]

34 minutes ago, Adsibob said:

our kitchen tap will make an intermittent gurgling sound

Sorry to quiz you but do you really mean the tap itself or the waste as the water in the sink drains away? Assuming the latter @dpmiller is possibly thinking the rainwater flow is creating a low pressure that empties your trap. There should either be a vent stack to prevent suction if the waste discharges directly into the sewer pipe or an airgap (pipe sits above an outside drain gully).

[Adsibob]

2 minutes ago, Radian said:

Sorry to quiz you but do you really mean the tap itself or the waste as the water in the sink drains away? Assuming the latter @dpmiller is possibly thinking the rainwater flow is creating a low pressure that empties your trap. There should either be a vent stack to prevent suction if the waste discharges directly into the sewer pipe or an airgap (pipe sits above an outside drain gully).

Ah, apologies. I meant the plughole/trap. I can see water at the bottom of the plughole move slightly as it gurgles, so I guess I was right about a pressure change sucking at that water. I'm fairly sure the pipe runs outside and before it discharges into the drain gully, there is an air gap. But maybe that's for another pipe. We have four sinks on the ground floor and this is the only one that makes this noise, I believe.

[Radian]

You'll have to trace its path then. Definitely sounds like a vacuum is being created. Apart from unpleasant odours finding their way up from the sink, the general sewage discharge may being adversely affected.

[Radian]

Do you actually have combined rain and foul water drainage from your property?

[Adsibob]

30 minutes ago, Radian said:

Do you actually have combined rain and foul water drainage from your property?

I’m fairly sure our rainwater off our roofs and patio are pumped into the sewer, yes. Where else would it go? I should clarify that we were renovating a 1930s semi so it probably had a combined system as opposed to separate rainwater and and sewage channels. But I'm not sure to be honest. Anyone know how i could check?

Edited November 2, 2022 by Adsibob

[Radian]

9 hours ago, Adsibob said:

I’m fairly sure our rainwater off our roofs and patio are pumped into the sewer, yes. Where else would it go? I should clarify that we were renovating a 1930s semi so it probably had a combined system as opposed to separate rainwater and and sewage channels. But I'm not sure to be honest. Anyone know how i could check?

Lift an inspection cover in a rainstorm or put a hosepipe into an accessible gutter? But I wouldn't bother. Houses of your vintage nearly always combine both drainage systems. If you can't trace the pipe to find out why there's a vacuum, you could just 'T' in a small AAV under the sink. Better to relocate the sink waste onto a proper stack though.