I need to completely detach the P-trap under a sink. The far end of the P-trap (i.e., closest to where the drain pipe runs horizontal and disappears into the wall) has a threaded, plastic fitting that just keeps turning. I thought once it reached this degree of “looseness”, it would simply detach. But, it does not. I am hesitant to yank it off, but is that the correct thing to do? It feels like it should be yanked, but I have a gift for making things worse. Can anyone advise me? (If you can tell me how to post a picture, I will post ASAP.)
OK, I think the problem is that one section of pipe has a beveled edge that must get compressed into another as the screwed fitting compresses the two pieces together. So, simply unscrewing the fitting (or, perhaps it is a union?) is not enough. Problem solved. (I admit, I had to go look at a new flexible P-trap assembly at the hardware store to better understand what was happening.)
The best part? Now you get to charge yourself $45 a half hour. 
Not so unreasonable.
When I successfully finished a similar home repair, I figured that it would have been close to $200 to have hired someone (even estimating that the professional could have done it in half the time I took), so I went out and spent that much on a treat for myself (additional compute hardware).
Made me more willing to try future home repair projects.