I am getting a new dishwasher and need to isntall it myself as the delivery people said they cannot install it because I do not have an air gap? On my current dishwasher the drain line goes through the floor under the house and attaches directly to the drain line. I was having some issues with my dishwasher leaving soap residue on the dishes and an installer said the drain line with no air gap is the problem. How do I correct this? People cannot believe I do not have a garbage disposal so they seem perplexed on how to install the air gap or even if I really need one???????