That is definitely the fuel tank drain. The shut off valve SHOULD be on the left side (the side you get on). You should be able to reach it standing beside it. Follow the fuel line back away from the filters. It is back about as far as the front of the fuel tank, kinda' tucked towards the frame. I can just get to it, as my arms are kinda' big. Seems I had to reach behind a line of some sort, possibly the large one going up in your picture. Between it, and the engine block. I know if you look back from about the fuel filters, you can just barely see the tang on the valve. That somewhat oily line near the bottom of the picture should be your fuel supply line from the tank. Follow it towards the frame. And as mentioned, you should be able to reach it from the topside.
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Just make sure you have about a half tank of fuel, or enough in the tank, to be above the bleeder cap on the secondary filter, or you'll never get the air bled out. Just did mine last Friday, on my 480C...