why do you 'feel the need' to clean the fuel system if it runs fine? IMO, those one-time additives may work by thge shock principle, but from what Ive read, the shock also causes repurcussions in the oil system, etc.
shock the system if it needs it badly, maintain it otherwise. 50% of the fuel in this country does not have enough or the proper additives to keep modern engines clean. Force it all out at once, and even if its just before the oil change, guess where it goes? Keep it clean a little at a time by boosting your fuel a bit, and youll be better off.
I dont always use fuel power at the 1oz/5 gal ratio every tank. I usually alternate tanks, filling up at 1/4 tank or less. Some times I add it every tank, others I skip. No rhyme or reason, all is well. If I had a dose in the last tank, and fill up from 1/4 tank levels, there is still a small amount of FP in the new gas, so its still boosting the additive levels a bit. I only buy name brand gas, so that quells my worries very slightly, and I know to use it fairly often, plus my system is clean to begin with, so there isnt anything to worry about. You might just add a dose every other week, or every week if you remember, depending upon how often your fuel up intervals are.
For a shock dose, Ive always liked a higher does of lucas (12oz/20 gal tank), FP (2oz/5 gals), BMW fuel system cleaner, redline fuel system cleaner (full bottle for the last two).
JMH