Most poly units are very easy to clean with the drain plugs located at the ends of the units. Simply push the drain plug in and, on most units, use the plug to plug the valve chamber outlet hole during cleaning. Thrifty King CT units are very well covered up and are a little more difficult to clean. Steel units must have the top cover removed to access the drain plug. An inexpensive toilet brush or similar brush can be used to swish the water around and remove dirt. Ask your local vet for animal safe cleaners should you choose to use one.
No. Water is always available to them with the valve and float keeping the fountain filled to the level that the customer sets it at.