I would say kava makes me pee more. Definitely diuretic to some degree. One thing the OP mentioned, brought back bad memories, about coming out of anesthesia and peeing. Had a horrible experience about 5 years ago. Had rather minor lumbar surgery, should have been released the next morning. Problem was I couldn't pee. At all. Drank water, ran the faucet, walked all night around the hall. Finally has to beg the nurse to put a cath in I was about to explode, the pain and agony. Talk about relief, hard to imagine actually begging for a tube inserted in one's wee wee. Apparently some prostrate issues were aggravated by the anethesia. Cost me a couple extra days in the hospital. Every time they removed the cath they had to reinsert. Finally left the hospital with a tube and a bag, and off to the urologist.
Stupid back surgeon, was giving me flowmax, said it would get me going in no time. Turns out it takes time for flowmax to work, it's not instant. Anyway, long story, sorry if it is TMI, but issue was resolved, everything flows as it should now. No meds needed.