I have an older home where the drain hose on the dishwasher is connected to a drain under the slab. I would like to eliminate this set up by running the drain hose to the garbage disposal like most any later built homes are. My question is, does it have to have an air gap between the dishwasher and the garbage disposal? Seems like in most later built homes, I never see any air gaps on counter tops next to the kitchen faucet.