Personally, my feeling is that PB piping of any kind belongs in the trash can, but since they are compressible, you can often tighten them until the meal parts meed. By that time the material is compressed out of shape. So the idealis to tighten them until they are snug and then check for leaks. If no leaks, leave it alone, otherwise tighten as necessary.: Its been sugested to me that poly lav riser compression nuts should be tightened until they cannot be tightened anymore, onyone disagree or agree. Ive always felt that they should be tightened until they dont leak and then a quarter turn. Any comments?