We had a leak from our water storage tank and in order to replace the platform that the tank was on, I disconnected all the pipes from the tank. There are three 22mm pipes that connect at low levels, and one 15mm pipe that feeds the tank near the top.
Now that I've removed the pipes, I am worried that the compression joints on these will not seal properly when I connect them again. What can I do to help improve the chances of making them watertight?
It's important to make sure that the olive fits exactly square on to the fitting and is completely clean. Any trace of dirt and you're likely to prevent a proper seal.
I'd not advise using PTFE thread-sealing tape over the olive itself, rather over the thread to which the nut is connecting.
I guess the answer is "yes, you can"; but be careful and gentle. Compression joints work by compressing the olive (like a finger/wedding ring) onto the pipe with the nut that covers it. Too tight and it deforms and leaks, not tight enough and it leaks due to a poor seal as a result of insufficient compression.
When re-sealing one of these, you have to get the nut ever so slightly tighter than it was before, without deforming the pipe. Liberal application of compound and PTFE over and behind the olive will help to make up for the minute differences in how it was sealed before.
I've done this on a number of the pipes in the two storage tanks and so far no leaks. We'll be checking for drips on an ever decreasing frequency starting every few hours and then to once a day, then every week until we're comfortable all is well.