Yeah, that's 64 million million million million miliion million million million million dollar question, ain't it. Most pipe stems are of the skinny kind, which doesn't always look right. And those that are of the thicker kind, don't always fit the tank neatly, alas.
My Musgrave currently has the Ephro True tank on it and the previously unused stem from the Guardian 1 40w epipe, which would've looked bang on...except there's a gap of 0.5cm between the tank top, and main body of the stem. I gotta find another tank that has a flush top for that stubby stem, me thinks.
I'm too knackered tonight, but i'll try get a piccy up tommorow, to show you what i mean.