Can anyone tell me whether PTF tape used on a compression fitting would degenerate? Also, where a plumber undoes the nut on one end of a compression joint is it correct that the connection at the other end of the joint will NEVER in any way be disturbed? The above queries may sound a bit odd but that is exactly what was said by an "expert" who attended my property after a very - and I do mean very - slow leak was discovered after a plumber undid and then a couple pf hours later reconnected a flexi pipe to an elbow connection. The expert said, in his experience, undoing one end of a compression joint will NEVER loosen up the connection at the other end and that PTF tape does degenerate and can do so within three years. Is he correct? Update ( I am new to this thread and I cannot see an option form me to comment on posts made so far) Thanks to those who have already responded. I should point out that the plumber says he did use a wrench to hold onto the elbow joint when he undid it and then did it up again. But what I need is independent confirmation that, even when the joint is supposedly tightly held using a wrench, the joint at the other end can still be disturbed. Also I am looking for comments which basically say PTF tape does not degenerate especially when it was used less than 4 years beforehand on the relevant joint.