I have had occasional bouts of diverticulitis and have found slippery elm to be very soothing and beneficial. I generally make about 250 ml of warm water in a glass, place in a teaspoon of honey and stir. Add 2 heaped teaspoons of slippery elm powder and stir to a smooth consistency. It's quite pleasant to drink. I take this first thing in the morning and just before I go to bed.
I have also found grapefruit seed extract to be very helpful and works quickly.