I would like to share with you a very useful procedure my colleague Shelly Prosko, PT described in her article "The 6 Stages of Toilet Meditation for Pelvic Floor Health".
I had never had chronic issues with voiding other than having the habit of evacuating quickly the first "package" just to feel more but have to end the session and walk/ do something else for few minutes till the urge comes again.
Probably something in the childhood, probably I rushed one day and the habit created ...
One day I will re-live that situation and dissolve that habit.
As a Physical Therapist that treated people with functional constipation, I can state that the ability to relax and therefore having the possibility to relax the pelvic floor is paramount.
For the advance pooper, one can go a step further after learning correct Thoracic diaphragmatic breathing.
The diaphragm's contraction downwards can aid in the relaxation of the pelvic floor in several way, including by the stretch it subjecting the pelvic floor muscles by creating the intra-abdominal pressure.
You can learn to activate the posterior fibers of the Thoracic diaphragm to push on the rectal ampulla, exactly as feces are evacuated in the last stage of childbirth.