Engine coolant

Hi

Replaced the engine coolant/inhibitor in a 1zh with new stuff, Had Toyota red stuff mixed 50/50 with distilled water, replaced with the same type but did not flush the cooling system. (yeh ok I'm a nuffy) The system was drained by way of the radiator and the engine drain plug so 99% has been drained out, I hear that problems can occur with precipitation etc if not flushed out properly and the two react or is this mainly with different brands of coolant being mixed.

Should I drain, flush the system properly and replace the coolant ???. Or the
miniscule amount left is the system won't affect the new stuff.

The new stuff has been in 2 days.

Phil