Let me ask this question, "Why air gaps?" it seem almost impossible that fluid from a backed up drain could get up into the drain line of your machine and contaminate it. I've pulled my hair out over the years with this issue. What are some people's thoughts on this?

Depending on where you're located the local governments take back-flow prevention and cross contamination VERY seriously. In L.A. County in California they have a whole department devoted to it. Some municipalities have attempted to require us to install a true reduced pressure back-flow device on each patient station! Fortunately, AAMI and IAPMO have waded in to prevent that. An air gap is the simplest form of back-flow prevention, but how many facilities have the water system drains and machine drains stuffed into a drain pipe of floor sink? Yuck!