First of all, 1 pint of soapy water mixed with 4.5 gallons on coolant isn't going to do any real harm.
Second to that, soapy water is what Water Wetter products are anyway. A little bit of surfactant to lower the surface tension of the coolant.
But lastly, I promise all of that soapy water is still in your coolant reservoir. Just siphon it out and move on. With this anal bunch
, I am sure you will be talked into using Porsche coolant only which is pretty expensive, not to mention how much of a pain it is to properly bleed your cooling system. In my opinion, it'll be a big waist to flush the cooling system over this.