And… as a follow on to Woof's great info, the tray you describe, while usually evaporating liquids draining into it, often doesn't do so efficiently resulting in mold and other gunk growing in the tray itself. Remove it (it's not attached to anything) from its holder and thoroughly wash and disinfect it.
The tray and tubing you describe really isn't for over flow of various liquids. It's part of the auto-defrost system (at least here in the U.S.) and is meant to drain away water that is left from the melted ice during the defrost cycle. Normally, there won't be any odor, except in cases such as you describe...