Yes.
Garbage disposal, if one is installed, or a wye branch fitting on the tail piece of sink drain. Dishwasher drain line should have an air break or air gap before the disposal or wye branch fitting.
End of clothes washer drain 1 1/2 - 2" above rim of sink it drains into.
The air conditioning drain is on the passenger's side of the firewall. If you do not have air pressure to blow into it to get it to drain then you might use something soft and flexible so as not to put a hole in the evaporator.
Yes, the air vent (air gap) is very much required!! It prevents water from traveling from the sink drain pipe or garbage disposal and into the dishwasher.
Did you happen to replace the disposal prior to this? A common mistake is forgetting to knock out the plug on the disposal, where the hose attaches, stick a screwdriver inside and beat it with a hammer to knock it out.
auk air gap
YUP Just make sure there is an air gap in the washing machine
Minimum distance of air gap
You can prevent your dishwasher drain from emptying into the sink by ensuring that the dishwasher drain hose is properly connected to the plumbing system under the sink and that there are no clogs or blockages in the hose or drain pipe. Additionally, installing a high loop in the drain hose or using an air gap device can help prevent backflow of water into the sink.
It sounds like the item you are describing is an Air Gap Fitting for the dishwasher. It is used to prevent sewage/dirty water from entering the dishwasher from the sink drain. Some Plumbing Codes require it to be installed. You can get kitchen sinks with multiple holes to allow you to install a sprayer and still have your air gap device.
You dont clean it as it is the unobstructed discharge from a faucet to the fixture other wise known as an AIR SPACE .... 2 times the effective opening of the discharge pipe BUT in no case less then 2"
Your air gap is not supposed to leak. Check the hose that leads from the air gap to the garbage disposal for a clog. This should resolve your problem.