I have a new basin tap to install. For reason of space/arrangement of existing pipework I'm planning to use flexible hoses rather than the copper tails it came with. The flexible hoses that I bought have two O-rings at the tap end. I'm just wondering - why two? Do you tighten it until the first one has disappeared down into the thread? Or until the first one is secure against the under side of the tap and the second one is still exposed. That doesn't seem likely but I'm not sure that I like the idea of forcing an O-ring into a threaded connection.
I remember just 1 rubber ring? Like this I saw this "Flexible Tap Tails 10mm x 15mm x 300mm 2 Pack" and thought of you! http://www.screwfix.com/p/flexible-...gclsrc=aw.ds&dclid=CNnIi5H89tICFaKg7QodS-YD8Q
Also, lubricate the rubber seals with silicone spray before inserting into the taps. Do not over tighten, they just need to be pinched up. Fit the other end to these from our hosts 69358 Don't put them straight onto a service valve, the sharp edges can split the rubber seal.
These are intended to connect from service valve or any other 15mm compression fitting, to mate with the end of the flexible tap connectors that have a 3/8" BSP thread which seems to becoming more common these days. FLTT38 Flexible Tap Adaptors 15mm x 3/8" 2 Pack (6089R)