Kitchen sink not draining, maybe airlocked?

[BorisUK2000]

I am hoping someone can help ... our kitchen sink stopped draining, it looks like an airlock somewhere. This is what I tried:

1. Used chemical drain unblocked and plunger
2. Took everything apart and checked all pipes
3. Bought endoscope and inspected all pipes all the way to 110 soil pipe - all clean
4. Replaced bottle trap (McAlpine C10V Anti-Vac). Also tried McAlpine S Trap
5. When the sink is full and not draining, I can push the AAV up with my finger, then the valve starts sucking air in and the sink starts draining. This is why I suspect the issue is with the airlock somewhere

This is our current plumbing, many thanks:

 

[Deleted member 120897]

Is this the only drain affected? Is the soil pipe vented or air admittance valve (aav)?

 

[BorisUK2000]

Is this the only drain affected? Is the soil pipe vented or air admittance valve (aav)?

Yes, this is the only drain affected. Everything else in the house drains nicely. I believe the soil pipe is vented into the loft (I know the others in the house are, but not sure about this one).

I don't think the waste pipe is blocked. I looked inside using endoscope. It is a large 110mm pipe which could take a lot of water. The sink stops draining as soon as the waste fills up, for example if I cover it by hand, fill up 5L of water into the sink and then remove my hand.

I am thinking about installing another AAV, just under the worktop, as per this picture. Do you think that would help?

 

[BorisUK2000]

Is this the only drain affected? Is the soil pipe vented or air admittance valve (aav)?

I forgot to mention, I removed the P trap and poured a bucket of water into the 40mm waste pipe and it was running nicely.

With the P trap connected, if I pour the same amount of water into the sink quickly, it blocks immediately. If I pour the same amount of water in slowly, it runs, as long as the waste is not fully covered in water.

 

[Deleted member 120897]

Is there an overflow connected to the sink waste?

 

[Ben-gee]

You are saying p-trap but what you actually have connected is a bottle trap, these are often really bad on kitchen sinks.
The first thing I would do is change your trap to a p-trap.

 

[Ben-gee]

I would also cut the waste lowdown to remove the two 90 bends and come straight up with just one bend at the top, make sure it’s a swept bend not a knuckle one.

 

[BorisUK2000]

Is there an overflow connected to the sink waste?

Yes, see this picture. A few days ago I found that the overflow pipe was blocked with black muck. I cleared it and thought that made if better, but will check again.

 

[BorisUK2000]

You are saying p-trap but what you actually have connected is a bottle trap, these are often really bad on kitchen sinks.
The first thing I would do is change your trap to a p-trap.

Sorry, I meant bottle trap. I also tried McAlpine Sink S Trap 40mm but that had the same problem. I changed it back to the McAlpine Anti-syphon Bottle Trap as the Anti-Syphon Valve did a good job stopping gurgling caused by the dish washer.

 

[BorisUK2000]

I would also cut the waste lowdown to remove the two 90 bends and come straight up with just one bend at the top, make sure it’s a swept bend not a knuckle one.

Thanks, I'll try that

 

[Ben-gee]

FYI I have fitted lots of sinks , I never use bottle traps or s-traps - always p-traps.

 

[BorisUK2000]

Thanks everyone for your input. I took everything apart and the soil pipe is indeed blocked, there is some mixture of grease, hair etc in there. The soil pipe goes underneath the house, probably 10m into the nearest man hole cover. I pushed 5m of garden hose in there, run water and it was filling up at my end. So the question now is, how do I clear it?

 

[exedon2]

Unless you enjoy getting filthy with drain goo time for the jetting team.

 

[BorisUK2000]

Nothing wrong with getting hands dirty
I have ordered a Karcher Drain & Gutter Cleaning Kit. Let's see if I can clear the fatberg using that. Wish me luck.

 

[WC1]

Im always in favour of someone who's game having a go themselves, let us know how you get on with the karcher.

 

[BorisUK2000]

So the Karcher drain cleaner worked perfectly. Soil pipe is clean now and the sink drains like never before. It took about 3 hours to clean 15m of very badly blocked 110mm soil pipe. Thanks everyone for your input.

 

[Deleted member 120897]

So the Karcher drain cleaner worked perfectly. Soil pipe is clean now and the sink drains like never before. It took about 3 hours to clean 15m of very badly blocked 110mm soil pipe. Thanks everyone for your input.

Well done you! I’m not sure it was going to shift it.