First of all, if you have an anal stricture forming (pretty common) or cuffitis, you need to have those addressed, as they can cause symptoms of sensations of incomplete emptying. These can come on gradually, catching you by surprise. And, if liquid stool passes easily, but you have difficulty the thicker the consistency, then these may be problems to rule out.
I am closing in on two decades with a j-pouch now and the main thing I have found that is helpful, is patience. I know it seems overly simplistic and stupid, but that is sort of it, for me anyway.
Much of the time I wait until the urge is strong, sit on the pot and a rush of liquid to sort of semiformed stool comes forth, followed by a blast of gas. Usually that means I am done. But, sometimes, particularly if I am on the dehydrated side, the urge is fairly strong, but emptying is not complete, especially if I do not get that last burst of gas. That is where patience comes in. I sit there a few minutes, read a bit, maybe check my emails on my iPad, and wait. I may lean forward, lean side to side, stand up and sit down, but I do not strain. Usually, after about 5-10 minutes, it just sort of comes. If I don't do this, I wind up coming back in in 30-60 minutes.
So, patience is a virtue, even if you do not feel like waiting for gravity to work. But, the pouch does need a gravity assist.
Jan