I’m lost

[Spectric]

My kitchen setup is a copy of the OP, I slide my 'Belfast sink' out after undoing the waste pipe

You must also be removing the waste fitting itself. I have the Armitage Shanks single sink in the utility and the cast in overflow gives me a 1 3/4 bulge round the waste on the underside of the sink, it had to go in before the worktop and I cannot slide it out so I made sure I used really good brassware without ceramic valves to minimise future problems with tap access.

My double Shaws sink has a flat bottom, really glad about that so I can slide it into place once the taps are fitted. Something worth noting is to always fit full flow isolators on the pipe work that are accessible, sounds obvious but I have seen a job where they were accessible until the sink was fitted !

 

[Lons]

If the drip is from the tap spout, how can you tell which side is leaking? Both sides feed the same spout so either or both could be leaking?

I'm not a plumber and have no skills in that direction. If this is rubbish, be kind!

That's a very valid point Bob. I really should have looked at the photo. Assuming the inlet pipes are fitted with isolating valves, which they should have been it could be done by turning one valve off at a time though.

 

[rs6mra]

I did change both valves
Next stop is to change the O ring on the outlet spout

 

[okeydokey]

Ah so not the tap washer, if it has an isolating valve for both hot and cold supply then turn one off and see if the taps still drips overnight - if it does try the other one overnight this should help decide which is letting water by and then as Lons suggests go buy a new entire valve

 

[Spectric]

Next stop is to change the O ring on the outlet spout

If the tap is dripping then either the cold or hot valve is letting water pass, changing the o ring on the spout outlet cannot fix it. If you have changed the rubbers and it still leaks then you need to use a tool to reface the surface on which the rubber washers seal.

https://www.cityplumbing.co.uk/p/rothenberger-tap-reseating-tool-70951/p/968917

 

[Daniel2]

If the tap is dripping then either the cold or hot valve is letting water pass, changing the o ring on the spout outlet cannot fix it. If you have changed the rubbers and it still leaks then you need to use a tool to reface the surface on which the rubber washers seal.

https://www.cityplumbing.co.uk/p/rothenberger-tap-reseating-tool-70951/p/968917

This is what I suggested back at the beginning.

 

[Oldman]

I recently had a dripping bathroom tap and thought it a simple job, stripped the tap head off, cut the seat, fitted a new washer, job done.
But it wasn't, the tap still leaked.
I had bought a 10 pack of washers off Ebay and on inspection against some I found in an old tobacco tin, the new ones were much harder material, so hard the tap couldn't seal.
I fitted one of the softer ones from the old tin and job done, tap is nice to use again.
So beware of no name packs of tap washers.

 

[Glitch]

Rubber ain't what it used to be. Ask any classic car restorer.

 

[rs6mra]

If the tap is dripping then either the cold or hot valve is letting water pass, changing the o ring on the spout outlet cannot fix it. If you have changed the rubbers and it still leaks then you need to use a tool to reface the surface on which the rubber washers seal.

https://www.cityplumbing.co.uk/p/rothenberger-tap-reseating-tool-70951/p/968917

I'll have to try a different tool. The one I got is a Draper which I thought would be up to the job.
Anything to avoid having to take the worktop and the sink out to replace the tap as the entire thing is all being replaced something in the Spring.