I found an old post about closing the pool for winter in this forum and it was discussed the easier method of just adding enough RV antifreeze to the main drain without blowing it out first and when the antifreeze starts oozing out of the main drain you just close and cap the valve for the MD. I will like to know if anybody have used this method and could tell how good it works? What will be any downsides? All I can see is advantages since its seems pretty easy to do without buying or using any shop vacs or compressors. 1 gal of rv antifreeze goes for about $3 or less.