Hi JBN and welcome!
If you're sure that you're ready to taper, and are prepared for complete abstinence from opioids, then a slow taper is the best way to go.
Depending on what dose you're at will depend on how much you drop by, and how frequently, but the main rule of thumb is to never drop more than 10% if the dose at once.
It takes between 7-14 days for your body to adjust to a drop in dosage, dependant on things like metabolism, so you should be looking at dropping weekly as a minimum, preferably 2 weekly.
Of course when you're still at higher doses you're going to find it easier to drop , and might be able to drop in larger amounts than you will later on.
What is your dose at the moment?
I'm sorry that your clinic don't seem supportive in helping you taper off, but clinics really have no financial incentive for 'keeping' a person there. They all have waiting lists, and can easily fill your slot with another paying customer. What they do have is a duty of care to you, so if they think you're not ready for tapering, that could be why they seem to be being obstructive.
Have you had drug free screens for a good long period of time, and been stable at the same dose for a good while?