I have a constant drip in my bathroom sink. After a little trouble shooting, I came to the conclusion that my hot water valve underneath the sink is the culprit. I traced the pipe down the wall, into the basement and to the water heater. The only thing between the water heater and the old valve in the upstairs bathroom are 90's and T's. There are no shut off valves. My question is how do I change the valve under the sink without having a shut off valve ahead of it? I began to try to do it without turning any water off, thinking I could be quick enough to put a new one on, but quickly found out I wouldn't be able to and now I'm stuck with the old valve still on and the sink still dripping! I have no more bright ideas (that's a joke, I know that wasn't a bright idea haha). I know there has to be a way, but I am trying to avoid costly fees of having a plumber come out.