I am not sure if this will help but thought I would share.
My J-Pouch has never emptied completely. Several years ago, my surgeon at Mayo Clinic suggested I start "irrigating" my pouch. They provided me with a good catheter and catheter tip syringe: 60 ML needle nose syringe which I fill with shower water while I am showering in the morning and/or evening. I insert the catheter in to my Pouch and then insert the water filled syringe into the catheter. My J-Pouch immediately starts emptying through the catheter, into the bottom of the shower/shower drain. I repeat this a few times until the output coming from catheter is clear. This has been a game-changer. Instant "relief." There may be new methods for irrigating the pouch now but this is so easy and literally takes a few minutes in the shower. No pain or discomfort at all. I think I posted a picture of my catheter in the past. I clean it with a little brush with some bleach when it starts to get dirty/discolored. (Just make sure I rinse it very well since bleach is involved). I buy the syringes from Amazon. You can use the same syringe for a good few months before you need to replace.