New bathroom sink waste outlet leaking

[sagalout1954]

Fitted new waste outlet to bathroom sink, (the sink has an internal overflow) the inside sink piece has rubber seal (and I've put a bit of extra sealant). Below sink piece has a rubber washer (one side flat and one side domed) and a large nut.

Doesn't seem to make a difference which way below sink washer is put on, seal is watertight. However, water is running down the thread (definitely - I can actually see it).

Have tried white 'plumbers tape' wrapped around the thread but makes no difference, water still forcing it's way out from there.

Any suggestions?

 

[easyflow]

Is the basin waste nut tight enough.
If so, dismantal clean off what you have applied, Spread some silocone onto the top part of the waste where it meets the basin and also spread some plumbers mate to the top of the washer being fairly generous (this forms a gasket and clogs the threads ) Tighten nut, this should be ok. If this is what you done before try it again.

 

[sagalout1954]

Nut so tight, surprised the sink didn't crack! Have since discovered there's such a thing as 'too tight' and could distort rubber washer creating the 'leak'.

Anyway, took your advice and tried again (made it about times but what the heck - no point in asking advice if we aren't going to take it - nothing to lose).

Put circle of plumbers putty (mait??) under sink but above the 'under sink' washer, keeping it tightly close to the waste thread (instead of on the outer rim of the 'under sink' washer like we had before), washer then nut, hand tight plus a small twist more.

No drips (except us)!

Read some old threads on here and appears this prob is quite common. A £1 basin sealer from B&Q (Robimatic) was recommended, also ditch the rubber washers in favour of plastic and some sealant etc etc. So plenty of further ideas if this hadn't finally worked.

Thanks very much for advice.