Doubling up fibre washer

[Adam78]

I'm trying to reconnect a bottom inlet toilet fill valve with a brass tail to a fixed water pipe.

I have one of those 1/2" red fibre washers from screwfix but they look very thin - about 1mm thick.

Is there any harm in sticking in 2 of these in before I tighten the connection?

 

[CBW]

Might not seal correctly and leak. If you don't like the look of the one provided then just use a different one.

 

[footprints]

AS long as it is a brass tail you should be able to tighten it up nicely it's the plastic ones that tend to strip if you need to nip up a bit.
Fibre washers tend to swell as they get wet the standard one should be fine.
The main thing is to ensure the pipes come together squarely even a slight angle will cause problems.