I made one a while back, and I will be making one soon for my new tank. Good Thread! Just a couple of things....

The 'Nards around here generally have a better selection than HD's that are always right next door. You just have to sometimes look harder sometimes at 'nards because they don't display the actual part mounted on the rack like HD does.

Is your container flexible at all? If so, I would be careful with just threading the fitting into the plastic and sealing it. Because if the plastic flexes the seal can easily break if the sealant doesn't make a chemical bond with both pieces. I would find a small fitting that has the female threads to the fitting you are inserting into your container. Then, drill the hole as Dave said thread the fitting through as Dave said, but stop a thread or two from flush. Then, screw the other fitting on the exposed threads on the inside almost flush and squeeze the epoxy9or whatever onto the exposed threads on both pieces and tighten. Then, you basically, you have a glued bulkhead.

Be careful with the small RO size tubing's. My RO unit has a slightly different size tubing than the 1/4" "ice maker" stuff that most hardware stores sell and therefore the fittings don't fit right. I had to get something called a "John Guest" fitting to properly fit my RO tubing. As you always should at any big box retailer, bring a small piece of the tubing you are trying to verify it fits.

I will post pics when I get around to building my top-off....