1. Figure tank size. I built my tank to go under my top tube, so I measured the available space from my head tube to my seat tube and the clearance from the top of my engine to my top tube. If you want to go behind the seat measure appropriately, or if you have a rear rack that you want to mount it on measure away. How much your tank will hold use the formula: Volume= 3.14 X Radius Squared X Length of Pipe. This will give you volume in cubic inches, google cubic inches to gallons for a quick conversion tool. Given my parameters I Built my tank out of 3 inch PVC and made it about 14" long. Volume = 3.14 x 1.5 squared x 14 or 98.91 cubic inches or .42 gallons 2. Cut PVC. I cut a piece of 3 inch PVC about 11 inches allowing about an inch and a half of length for each end cap. put end caps on to make sure it fits in the desired location adjust length as necessary, but don't glue yet. 3. Add fittings. I used a step bit to drill a hole in one end cap. The step bit allowed me to make the hole slightly smaller than my fitting, and with a little bit of muscle I was able to thread the fitting into the pipe. I used scd 40 PVC it was plenty thick, Scd 80 would be overkill. I did the same for my fill pipe fitting on the tube. 4. Glue it. Use Seal All or some other fuel proof adhesive/bonding agent/ glue. Unthread your fittings apply glue and re install. Glue end caps on. 5.Vent Cab I used a standard brass garden hose cap, drilled a hole in the center then inserted a slotted peice of plastic (sHeet metal would work as well) see pictures below. Materials list for fittings will be in following post. I plan on using a universal shut off kit found at Lowes instead of a petcock to shut off fuel, it will be in materials list.