Grumps wrote in :

On 27/04/2020 18:56, John wrote:
If only people would realise that it is the gasket that created the
seal - the tread it sher to pull the faces together - and what about
a smear of coppaslip?

Indeed. I'm not a plumbing expert, but that's how I understand the
situation.
The immersion manufacturers that I've read installation instructions
for say you should only need to use the supplied gasket; no thread
sealer is needed. One did suggest using PTFE as a lubricant.




So many plumbers and others seem to want to use sealants and gunks on all
threads - perhaps it adds to the mystique of the trade and gives them more
work in the future when things won't come apart. Same wit compression
fittings. The thread is there to apply a clamping force. Cleanliness is the
most important thing.