It takes 30 seconds to remove the dip tube. And if their cut down like mine are, they will fit under the lid. Then I just fill with hot water and oxyclean.
If your lazy, fill with hot water and cleaner, put lid on, and hit it with a little co2, then GENTLY depress the poppit, it will fill with cleaner. Just remember to depress the poppit when emptying, it will hold liquid when the kegs drained.