Being Clean and Lubricated
Making sure you anus is clean can be as simple as wiping the outside. Most people want to go further than that and make sure the anal canal and the rectum are clean, to some extent. How to and how much you should clean is covered in great detail in the article Eating and Enemas for Clean Anal Sex. But there is a significant side benefit of squirting a little water up your ass that constantly overlooked.
Most commentary on anal sex and lube start with the principle that the anus and rectum do not lubricate themselves. That is false.
The microanatomy of the wall of the rectum is similar to the rest of the gastrointestinal tract; namely, that it possesses a mucosa with a lining of a single layer of column-shaped cells with mucous-secreting goblet cells interspersed, … – Wikipidia
The truth is that the rectum does not secret copious quantities of mucus all the time. If it did, your ass would be constantly leaking. But it does secrete enough to let stools pass easily and painlessly through the rectum and out the anus unless you are constipated.
The walls of the rectum are always lined with mucus. However, unless you need to relieve yourself, it will be sticky or tacky. The mucus will become slippery if you wet the mucus by injecting a small amount of water into the anus. You eliminate any fear of things that go in are going to come out dirty as well as activating your anus’ and rectum’s natural lubrication. Of course, with repeated flushing of the anus and rectum, the mucus layer can be washed away. That is where injecting lube solves all problems.