Put antifreeze in black and grey after winterizing ?

I end up with antifreeze in the grey tanks, not as a tank protection issue but as a "byproduct" of good practice in winterizing. you do NOT want a P trap to break, and the common and easiest way to make sure that doesn't happen is to pour antifreeze down each drain to fill the p trap with antifreeze. and to insure each is filled, excess will be needed and end up in the grey tanks.