The Truma Replacement O Ring Kit for the Ultraflow comes with two different sized pairs of  ‘O’ rings to accommodate the two different inlets. The instructions are included in the kit and state the following for correct fitting. Please check the pistol grip to see if there is a number 2 in the moulding as per the diagram. If the number 2 is present then use the pair of smaller ‘O’ rings contained within this pack, if there is not a number 2 present then use the two larger ‘O’ rings contained within this pack.