You're right filter does go on the low pressure side. I have a friend that had a Latham single system that did not use a reservoir either and he had no problems. But I do understand what Tom was saying that you need one. One cylinder will be unequal displacement and the pump reservoir will have to be balanced to be almost empty or almost full depending on way you are turning. I would fill it up run it and see how close to the edge you are. Obviously it was ran like this, just might not be optimal.