I had my j pouch created in 2014, I'm due for takedown within a couple of months; after surgery I stayed in hospital for 15 days and I too had no control whatsoever, certainly wasn't pleasant.
Once back at home, for at least two weeks every time I had the need to urinate I had to evacuate the mucus too.
Like yourself, I too had no control, I wasnt actually incontinent, like I was when in hospital but the slightest movement, sitting down or climbing the stairs, whatever, I could feel a discharge taking place.
I had to take extra precautions during my sleep too and many a time I awoke to a very unpleasant mess.
This only lasted 10 days, maybe 14 at most before my output was under control, although it seemed like forever at the time.
I still experience a mucus build up but I have total control, without leaks or any emergency runs to the bathroom.
I can confidently get out and about for hours on end without any cause for concern.
I dont think the cause is due to weak muscles, it's just a build up of fluid in a very short time that needs to get out.