Everything they just said. Tubes aren't the place to economize for gl. For dipping in paint or stain, maybe, but not gl. I did make up one in pvc for stain, and you can even attach adapters to go to a bigger size sort of reservoir thing at the top. For gl though, the gasket lids are what you gotta have, and I don't think there's a pvc fitting that matches those lids. Then you'd still have to buy the rubber gaskets, and they don't sell that rubber at the hardware store. Just way more trouble than it's worth.
If you get some of the genuine gasket lacquer like has been suggested, that stuff needs to be at room temperature, otherwise it wears the gasket holes out faster, and is a lot harder to pull through, just because it is so thick. It is great stuff though.
Tom