Loft tanks and connection to mains supply

[Fishing Badger]

I have the bog standard tank in the loft, last weekend half the ceiling came down and I discovered the outer joint from the mains supply to the ball cock plastic pipe was leaking. In order to stop the leak I replaced the washer in a compression type fitting with a black rubber O ring (local DIY shop). Copper pipe has a flange which the plastic pipe butts into and the washer makes it watertight when the nut on the pipe is tighten.


I've since been told I've used the wrong type of washer, it should have been a fibre washer.

At the moment it seems completly sound and dry.

Which is the correct washer type ?
Are fibre washers waterproof and don't they rot over time ?
Do I need to replace O ring quickly or will it last ?

Don't really want to repair everything only to have it happen all again just because I've used the wrong washer.

 

[gas4you]

Traditionally tap connectors, which is what you have, always had fibre washers fitted in them to seal the joint, Modern plastic push fit tap connectors have a rubber washer in them.. I can't see no problem with your 'o' ring lasting as long as a fibre washer