The "drain washer" looks like a normal washer, but it is not. It is a "crush" washer made from very solf alloy. It is designed to crush a bit when torqued. Theoretically you should change it every time. I don't. If it is deformed or significantly crushed, I do. How do you tell? Buy a new one and compare the old one to it as to size, shape and thickness. If they are the same, use the old one.
Usually you can get them much cheaper at an auto parts chain than at a bike shop. And many brand bikes use the same washer. Again, compare the size and save money. Even at a bike shop Honda or Yamaha washers will be much less than Triumph.
Monte
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