Below are a few examples of when you can use the above plumbing items:a). You are re-using an old olive with a new fitting.b). Putting a new olive onto pipework has been compressed slightly by an old fitting.c). Fitting a compression joint in an area where it will be difficult to reach once it is fitted.d). With the joint is leaking, despite (or possibly because of) your best efforts to tighten it. ( Highbury Plumbers use these compounds and tape).In these circumstances there are a couple of ways to approach it. Firstly, taking a length of PTFE tape and wrap it around the olive 3 or 4 times, then re-tighten the joint. The tape will help the olive form a waterproof seal even if it’s previously been tightened too much. Alternatively you could use a jointing compound rather than tape. The advantage is of this is that the compound is a paste and as such is often easier to apply than tape. A Highbury Plumber uses PTFE tape. To apply the jointing compound just put a small amount on your fingertip or a small brush and smear it over the olive, making sure you get it all the way around the joint. Be aware that there are a number of jointing compounds that are fine for central heating systems but harbour bacteria that can infect drinking water. So when using jointing compounds, be sure to check that they are safe to use on drinking water, or (potable) water as it’s often called. Jet blue is a popular compound for (potable) water whereas jet White can only be used for non-drinking water. Plumbers hemp used to be used as a washer or as a jointing compound. This also attracts bacteria and should not be used in drinking water.