A tip given to me by a rehab nurse years ago. When you go for a wee, after you think you’ve finished raise yourself up off the seat a few inches. The retained wee will come out. Do it two or three times if you need to. It’s not just your bladder that retains urine, the ‘pipe work’ does too.
Homemade barley water will not cure bladder inflammation but it can help to prevent recurrences. It’s roughly half a cup of Pearl barley to 5 cups of water. Rinse the barley under the cold tap, put the barley and water in a pan, bring to the boil and simmer for 5 minutes. Drain the water into a jug and you can use the barley in cooking. It is a bit like thin wallpaper paste but a spoonful of honey and a squirt of lemon juice make it taste better. I tend to just hold my nose and gulp it down!