Hi All

I am fitting a new bathroom sink. I usually do this by fitting an isolation valve (one where you turn it on / off with a flat head screwdriver) between the incoming supply (terminated with a tap connector) and the flexible hose to the tap.

I am having trouble with one that constantly leaks no matter what I do. The tap connector side is fine but the connection with the flexible hose leaks. I have so far tried the following
1. The tap and hose came with a filter type rubber washer so used that first
2. Tried replacing that washer with a normal flat rubber washer
3. Put PTFE tape on the thread and used the washer.

All options still result in a leak. It looks like it is coming from the centre of the nut (as opposed to the thread) but can't be sure.

Anyone have any ideas what could be wrong?

Thanks

Lee