The reason that the hot water tank retains antifreeze is the
configuration of the chamber. It is essentially a box with a coil, the
coil containing the exhaust water from the engine. The 'box' has a
large internal surface area and cannot be totally drained and there
will usually always be some fluid trapped at the bottom. The only way
to rapidly dilute the remaining anatifreeze is NOT by running zillions
of gallons of clean water through it as the 'configuration' inside
which promote 'hydrodynamic dead zones' ---- meaning that the flow of
incomming water doesnt necessarily fully mix with and dilute the
contaminent..... its a hydraulic engineering 'phenomenon/problem'
common to 'most' tanks.

If you have anti-freeze the best way to 'clear' it is to do 'alliquot'
washings:
fill tank, mechanically drain tank (remove the coupling to the outlet
fresh water nozzle and let drain), fill tank, mechanically drain tank,
etc. etc. etc. ditto, ditto, ditto. In this manner you will
mathematically (exponential decay) dilute the 'residuals' FASTER than
by blasting the entire Atlantic Ocean through it .... and still have
antifreeze left in the tank.

If you are throwing out the water filters after only 2 or 3 fills,
then you are absolutely wasting your money. Such filters in
*continuous service* typically will last for MONTHS (depending on the
'dirt load' already in the water ..... thats millions of gallons of
water. Well water is usually quite clean but municipal water is
probably one of the "dirtiest" fluids on the earth. When to change a
filter: when the pressure drop across the filter changes by approx. 10
psid or the flowrate begins to decay.

For sanitizing the tank (no visible bacterial scum, etc.) the BEST
cleaning agent is peracetic acid ..... obtain if from suppliers of
Reverse Osmosis equipment. Its quite safe to the environment (degrades
to 'vinegar').
For Disinfection (noticable bioburden) mechanicall scrub with caustics,
then strong concentration Chlorox (solution of 25 parts per million),
etc. .... then peracetic acid.

Dont let a filter (or boat water tank) sit for long periods filled or
partly filled and unused .... Why grow the stuff that you dont want
in there in the first place. ..... if you let a glass of tap water sit
open on your drainboard for a few weeks, you wouldnt drink it. Why do
people do this with 'boat water'?

The water 'specs.' used in the "RV" industry are out of date (by
industrial standards) by about 50 years. These are 'derived' specs.
from an 'active or flowing' water system ..... and those who derived it
made GREAT mistakes in not ackowleging that a RV or boat has an
inherently STAGNAT water system ..... best damn place in the world to
grow bioburden.