You are looking after which material water tank? I have stainless steel water tank with the same capacity as per your requirement. It was specially made by special order to Industrial Tanks & Storage | Great Basin Industrial and it is very rough and tough. If you need it, you can let me know...
It is advisable to clean out the tank periodically. How often depends on fuel quality and even tank material, but every couple of years you should at least draw some fuel from the very bottom of the tank to check for water and/or sediment. You cannot do this through the pick-up tube feeding the...