Selgas
If the cylinder is older than 5 years then Rheem recommend that the anode be replaced to enable it to carry on protecting the cylinder from corrosion – be careful that you replace it with the correct one – which is usually identifable by the colour on the top of the anode screw in nut.
As far as cleaning out the cylinder – flushing is by far the best and safest way to achieve the desired result. By using any product other than just water you carry the risk of damaging the connection pieces and the interior walls of the clinder.
Hope this helps. 
Selgas Services Ltd
Craftsman Gasfitters, Plumbers, Electrical Service Technicians
