 It is probably clean enough. Look in with a flashlight when it's dark outside and you will see any crud. I would probably leave alone. If you want to clean it you can get a rag and stick and after that put some clean fuel in and roll around and then dump empty till you are happy. I use a double filter arrangement with a water filter and a separate regular filter and this has worked for me for decades. I add Stanadyne fuel treatment. In thousands of hours of use of many tractors I have never even had to remove an injector. Oh...yours is probably 000 gallon. Not many 000's around. 