I have found the Sun Mar Excel Non Electric to be an excellent unit and have had it in use for 4 years. It is largely maintenance free even though it is being used in my rental property by up to 5 people per week. Even the emptying job is not as bad as you would assume  due mainly to the fact that most waste has been reduced to almost nothing. I continue to be a compost toilet convert! I have found toilet revolution service to be first rate and most helpful. Patrick has always got back to me with answers to my various questions.