Designer 35RLTS and Jayco Talk...Thanks Frank!!

On my Eagle , I had a problem with these drains . No matter which way I turned them , they did not drain . Stupid me , I did not PULL UP on them until last year . It was beneficial that I did use anti freeze to winterize , as enough worked through those lines to protect them . QUESTION ????? What is the best way to prevent from blowing the "O" ring from the city water in let while winterizing , I have forgotten again how to do this. Thanks.