Aloe to the rescue. I like to dilute a little with water and use as a wipe.
Also, shea butter or something soft will help protect the tissues down there.
You experience "burning butt pee" as we on the zone like to call it. It comes from passing old toxic bile so it is good you are passing some of that old bile. Use the shea or oil as a barrier and it will be better.
You won't always pass the old toxic bile, just take a little precaution just in case.
A bath after the flush helps too. Use the shea after you dry off.