The trick to this is to get into a position that elevates the insertion (think sitting upside down).
1. fill with warm water
3. Squeeze the bulb and hold it squeezed while pulling it out.
4. Release the bulb.
repeat 2-4 until water is empty.
5. either hold position 5 minutes or as long as you can stand.
6. evacuate and repeat until you feel clean enough.
Ingeneral, don't do this immediately before anal sex, It is best to have a few hours as this will remove natural lubricants as well.