Because the engine block has no drains, you can only do a partial drain. Poor coolant chemistry only shows up months later as corrosion and loss of cooling efficiency.
Since you can't drain all the coolant, doing a chemical flush very difficult without destroying the coolant chemistry. You will never know how much flush chemicals are still left in the system. If you do ample water flushes to remove the chemical flush, you still don't know how much coolant to add to get a proper mix.
What I did on my 2002 XLT, was to drain and refill several times without a flush. I pre-mix 50/50 with distilled water in a plastic measuring jar prior to filling. That drain and refill does waste coolant, but perserves the coolant chemistry.
If you know the total coolant capacity, you can do the math to see how many drain and refills are needed to replace 95%.
So far my coolant system has never leaked or had a pump, thermostat failure.