Different Century - Different Answers
In the 'Old Days' (long before ingredient disclosure laws) I heard Prestone Flush was simply powdered Oxalic acid (teak wood cleaner), neutralizer (baking soda) and a fancy yellow plastic tee with cap you cut into the heater line and left permanently installed (hoped for at least by Prestone) with successive applications of the same $3.49 price of the total kit price. Yes, I bought it and used it like everyone else back then. It seemed to work, but everyone drained their AF into the stormdrain every year or two when we didn't know it killed dogs and 2 gallons only set you back a whole $3.50 including tax.
Regulations what they are today you're likely getting some (as you say) 'non-acidic' non-phosphate version of TSP - and of course baking soda afterward. I recommend doing a dItpot full of search and "just use your best judgement, Joel."
The surge tank is just a big plastic bottle. Unbolt it from the car and clean the living vrap out of it with whatever you want. Muriatic Acid (aka pool acid, soldering flux....), or magic purple, Bleche-White, TopJob, CLR....
Methodical flush process and burping the system for air is equally important to simply getting the old rotten acidified garbage out of your engine and radiator every 5-10 years.
\'96SS SOB: SSRI, Herter Tune, Tri-Y II, , 3000 Edge, F/HO bars, METCO extendeds with CV MMC, Bilsteins, currently Vredestein Ultrac Sessanta (315/35 rear). Finally, wait for it... LT-4 knock module!
\'96FWB BUW-Butt Ugly White: PCMPerformance tune, HDFA w/ swissed filter, 1/2 SLP s.s. catback with H- and Flow Super 50s, oem opti rebuilt 3 times, SS Bars, METCO LCA, Airlift 1000, Monroe SS, PowerTrax No-Slip, CTS wheels with +1 rubber. Finally, yes again... LT-4 knock module!