I need to joint copper pipes in a straight line. Off from the wall when testing, the coupling fit into the pipe tight but ok. However, when up in the ceiling, it is extremely hard to put the coupling totally onto the pipe, it can goes in only about 1/8". It is probably because it is slightly off the straight light. I try to wiggle it, twist it, nothing works. Is there any trick and tips how to put the coupling on to the pipe?