"The shower or bathtub is a good place to begin. (By the way, contrary to what you may have been told by family and friends, a healthy person's urine is STERILE as it leaves their body. Once outside the body, airborne bacteria can contaminate it fairly soon, so be sure to rinse the shower or bathtub surfaces with fresh water)
Don't expect to master this skill on your first attempt. After you've practiced a few times, you should see some improvement. (aim for the drain) "
I have found it helpful to do the stretching exercises my physical therapist recommends. Do some core strengthening exercises, such as the ones highlighted at The Mayo Clinic. By keeping your core strong, your back won't put itself in a position to cause that sciatica pain you are having.