We have purchased two 1/4 turn angle stop valve to put under the sink in our bathroom, the old ones where leaking. We have tried to put the copper ring that comes with the new valve in put then we are unable to tighten the valve to the pipe. We have tried plumbers tape to try and seal it but we still have a drip, It's small put it's still dripping. What are we doing wrong and is there another way to do this? Thank you:confused: