Douching is the practice of cleaning the bowels some time prior to sex by filling them with water then expelling that water. It is a way of ensuring the rectum is clean, which some men prefer when having anal sex.
You can either use a bulb syringe – i.e. without the sticky-out bit – or an enema bulb or specially designed shower attachment. You can buy liquids intended for use as enemas, but water is said by many to be best. Plain water. Never use soap.
Lubricate your anus and the syringe/bulb/attachment – and insert. Relax, just as if you were taking a penis or toy. Squatting can also help easy passage. You don’t need to go in deep, just enough to get through the inner sphincter.
Squeeze the bulb or turn on the water – gently, and with pauses – until you feel full.
Hold the water in a few seconds. Add more if you don’t feel properly full. Some of the water you use will be absorbed and you may need to pee – and then add more. Enjoy the feeling of fullness.
Then expel. You might wish to do this in the shower or bath, though solid matter may emerge, or over the toilet. If in the bath, it can help to make sure the plug will allow solids to pass through.
Repeat two or three times, then you’re done. Shower off, and allow a couple of hours prior to sex for the mucosal lining of the rectum to be re-established. Yes, it needs planning ahead.