However, when you do you will lower the octane of nominal 87 octane e-10 gas to somewhere around 83.5. You will need a LOT of octane booster to get the gas back up to 87. In theory you could start with premium grade gas and wash the ethanol out of it to get residual gas close to regular grade without putting any additives in. Another consideration is what else will you be washing out of the gas. Any component of the gas that has some water solubility will be washed out of the gasoline to some extent. Gasoline is normally a mix of approximately 15% C4–C8 straight-chain alkanes, 25 to 40% C4–C10 branched alkanes, 10% cycloalkanes, less than 25% aromatics (benzene less than 1.0%), and 10% straight-chain and cyclic alkenes (from an ACS reference). All of those components have different solubilities in water, so when you wash out the ethanol you also wash out different amounts of the gasoline components and change the composition of the base gasoline. You will also have the problem of what to do with the solution of ethanol you wash out of the gas. You can't just dump it since it will contain some gasoline components. Finally, washing the ethanol out of the gas will dissolve water into the gas (around 0.5-0.6%). You really should remove that water by filtering the washed gas through water trapping filters.

From a chemistry point of view, the article has some problems since they neglect the positive volume of mixing of ethanol with gasoline and the negative volume of mixing of ethanol with water. They also don't address the effects I mentioned above. That said the basics are correct.

Another consideration is that by acquiring the gear you need to remove the ethanol from gas safely you may put yourself on the map for drug enforcement agencies. Just imagine the fun of explaining what you are up to when the local SWAT team raids your garage to find you in there wearing a tyvek suit and respirator while you play with your new chemistry set.