Blocked sink… but not obvious where the blockage is

I’m hoping some wise people will be able to help me.

Our kitchen sink and dishwasher are attached to the same drain. Flow has been slow for a while, but recently is very slow and the sink will take ten minutes to empty.

I have dismantled the fittings under the sink and they are all totally clear.

I used a 7m long drain snake today. It went to its full length, with much rotating and agitating. The flow is no clearer.

What are my next steps?

I'm guessing there are other drains that connect to the problem one within 7 meters?  Do they drain slowly or are they fine?  If they work well and the sink doesn't, and you're sure the snake did it's thing, maybe the problem is on the venting side?  Not sure how your plumbing works in the UK but here we have vents near most fixtures to let air in as the water drains downward.  Maybe a vent got plugged up on the roof?

Good point about other drains. The shower - which is more than 7m away - also drains slowly at times. But that has always seemed to be a local issue, fixed with a slug of bathroom drain unblocker. I've put that down to wifely hair gunking in it up. But it is quite possible there is a blockage in the shared drain.

I've no idea how air vents would work in this place. I'm not sure where I would start to look for them. It's an old building and everything was retrofitted by previous people.

If you follow that drain, ideally you'll come across a cleanout somewhere before it gets buried and becomes inaccessible. From there, you should be able to snake in both directions and see if you can hit the clog from there. If you have any fixtures lower in the house (like a basement laundry sink) and that doesn't back-fill with water while waiting for the kitchen to drain, it means the clog is somewhere between the sink and where that lower fixture joins the main drain.

What Jeff said!

For the shower drain you can use these.

Do you by chance have a garbage disposal unit under the kitchen sink?   If both the diswasher and adjacent sink are slow, but there is no water backed up when the pipes under the sink are remove, I would suspect a a disposal unit.  Not sure if there is one in play or not, but they will often cause a slow drain that clears up after a few minutes.

When you used the snake were the pipes under the sink in place and was there water backed up?  Did you snake down through the pipes with water in backed up and no sign of increased drainage?

There is an enzyme product that works fairly well.  It introduces biology to the pipes that feed on clogs.  Often a partial clog can be cleared biologically.

Jack Edmondson wrote:Do you by chance have a garbage disposal unit under the kitchen sink?   If both the diswasher and adjacent sink are slow, but there is no water backed up when the pipes under the sink are remove, I would suspect a a disposal unit.  Not sure if there is one in play or not, but they will often cause a slow drain that clears up after a few minutes.

When you used the snake were the pipes under the sink in place and was there water backed up?  Did you snake down through the pipes with water in backed up and no sign of increased drainage?

There is an enzyme product that works fairly well.  It introduces biology to the pipes that feed on clogs.  Often a partial clog can be cleared biologically.

No disposal unit. They are uncommon here in the UK.

I ran the snake twice. Once dry and once with water in the pipes. It didn't speed drainage at all.

Jeff Sullivan wrote:If you follow that drain, ideally you'll come across a cleanout somewhere before it gets buried and becomes inaccessible. From there, you should be able to snake in both directions and see if you can hit the clog from there. If you have any fixtures lower in the house (like a basement laundry sink) and that doesn't back-fill with water while waiting for the kitchen to drain, it means the clog is somewhere between the sink and where that lower fixture joins the main drain.

I'll take a poke outside in the morning and see what I can find. I'm not optimistic, as there is a bunch of stuff about this house that is less than ideal!

Hi Michael;
Are your drains feeding into a septic tank?  Or city sewer lines?
It may need to be pumped out if it is a tank.
Even worse would be a drain field plugged up beyond the septic tank.

And, if you're on a gray water system, check the outlets. Two years ago, a mouse chewed through the cover on one of ours, got in & trapped. He formed a perfect little snag, for every hair, glob of goo, and layer of soap residue that came down, and blocked ours, badly.

thomas rubino wrote:Hi Michael;
Are your drains feeding into a septic tank?  Or city sewer lines?
It may need to be pumped out if it is a tank.
Even worse would be a drain field plugged up beyond the septic tank.

City sewer - no greywater or septic involved. Everything else is draining freely.

That is good news, Michael.  No septic or drain field eliminates a huge portion of your potential problems.
A city hookup should have a cleanout port inside the basement or under the house.
You could have a tree root plugging your outside line.
As suggested earlier a venting issue can cause slowdowns, although having had vent issues they usually have burping or gurgling noises accompanying them.
I suspect that something was flushed down a toilet (Barbi doll) went as far down the pipe as it could and lodged.  This could have happened years ago and has taken this long to back up.
You may need to call in a plumber with a long power snake.