As I have formulated products for 20 years, perhaps I can add some clarity.
On a cost basis the Walmart product has to be ethanol. It is the only non-toxic product that could come in even near that price point. Another problem with ethanol is that it evaporates. What is the best product?
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Head. Depends on the brand. If Jabsco (stiffens neoprene parts) ethylene glycol is best, Rairitan (nitrile parts) propylene glycol is a little better. Alcohol is going to be bad for "white" sanitation hoses (increases permeability) and butyl. The best choice may be draining, which is what some manufacturers specify, but EG is the safest bet; just don't drink the blackwater.
Automobile. Very brand-specific, as it depends on the alloys used. I formulate AF products and there is no true "universal" formula, despite some marketing claims. That is a matter for the courts. However ALL OEM AF formulas are EG, which is OK and engines and blackwater but not potable systems.
Raw water impellers. Again, it depends on the material. Pure Oceans can damage (stiffen) neoprene impellers, whereas EG is OK. PG is OK on nitrile impellors... but the flex life of nitrile is not as good. Your expereince will depend on which you have. Do you know? Do you know your hose materials?
Filters. PG can craze nylon very badly in a few winters. Also ethanol and to a lesser extent, EG. Removal of casings is better.
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No universal rules, guys. Study the materials of YOUR systems.
And all 3 of these products are effectively non-toxic to fish, according to EPA and DFW.