I used this for my HLT. Lowes had the 1/2 or 3/4 inch stainless washer, so I just went with the 25 cent zinc coated washers. I used 2 washers on the outside, but the handle hits the cooler, so I do think I need the 3rd washer. I had a few white washers hanging around that fit on the outside, so I didn't need the O rings - I bought the wrong size anyway. Apparently these were sold by outside measurement(?) I didn't have any leaks, but heard a cracking sound when I put the hot sparge water in the cooler.
This was my 1st time using a 3 level sparge. It sure beats sparging with a sauce pan.