Fixing a leaky sink

After Taylor Wimpey sent a clown of a sub contractor to refit a kitchen worktop, it has come to my attention that the sink has started to leak.

I’m trying to figure out how to fix it. The leak seems to be from where the seal directly beneath the plug meets the drain/waste pipe (not sure what the term is). I’ve checked YouTube which seems to suggest replacing the kitchen sink strainer and using plumber’s putty to seal it.

Is it likely the cause of the leak is due to no putty being used when it was installed? Or should there be some sealant around the rubber gasket below the sink? None of the videos suggest using sealant around the gasket.

Thanks for any help folks. This thing is doing my head in and I could really use not having to pay £100 to a plumber to come and fix what is likely to be something simple.

Can’t you a) get TW to sort out their mistake or b) just tighten the nut up a bit?

If it’s tight and the rubber is below the bowl then you don’t need any sealant on the sink side. Best practice would have putty or silicon to keep the food debris out and it hygenic.
You may find a leak at the brass tail if no PTFE tape was used or at the slip/compression but where it connects to the plastic pipe (per North American install, not sure if UK ideas same)

Someone’s coming, but it’s on Monday. It’s taken nearly 2 years for them to fix the fudgepacking worktop in the first place.

I can’t see a nut from the top to tighten up. I think I’ll have to remove the “U” shaped pipe to tighten anything up.

@dirksdiggler so a bit of Plumber’s Mait/Silicone above where the rubber gasket meets the underside of the sink? Trying to think ahead and see if one is better than the other.

The strainer is likely the “nut”.

My belt and braces approach:

Undo the trap (bucket underneath).
Put long screwdriver through strainer. Hold to stop strainer spinning.
Undo nut from tail.
If tail is loose, then thin head of silicone to seat in sink.
Refit rubber washer with either plumbers mate or silicone between it and underside of sink.
PTFE tape around threads of tail.
Tighten nut (remember screwdriver trick).
More ptfe tape where trap will attach.
Screw trap on.
Wait for silicon to set.
Test.

do nothing.. you havent a clue and neither have many of the posters.. no stress required.. mondays not that far away..

you take it apart lather it with silicone or ptfe and the forst thing the fellas gonna say… ”nowt to do with me pal.. cheerio!”

£100 to fix.. its a 25 quid max job to put right..in and out in 10 minutes. leave it till monday..

Yeah, pop a bowl under the drip and wait.

If you use sealant or putty you’ll never be able to get a good fit should you ever have to replace the waste trap.

Managed to do more or less what @ourmaninthenorth suggested to stop it leaking. It’s held up so far.

@totaishell was leaning towards your suggestion. Problem is between them coming to inspect on Monday and then deciding to fix may be a long way away given my experiences with them!