Ah, creeping right along... an HW75? A real oldie but goodie. I owned a 2nd cousin twice removed, an L-4, for a while until Hurricane Andrew trashed it. And of course Stinson ultimately became part of Piper, so we were part of the same big aircraft family. Do you fly on skis during the Maine winter?
I admit the thread creep and mild rants really don't bother me much, and actually (to me) add something to the social karma of the forum. I'm not crazy about the personal attacks, but every long-lived forum I participate in has them, so I've learned to tune them out. One forum did have a specific almost-no-holds-barred area called "The Cage", to which offensive posts were moved, and some posters restricted (a "time-out") until they agreed to play nicely. It was a pretty entertaining area to visit.
Back to gravel, I found 2 bags of store-bought gravel in my shed as I prepare to overhaul my system. One looks like Florida Chatahoochee stone: rounded, mixed shades of brown; the other is sharp-edged, uniform and white. I guess the ideal underbedding wound be perfectly round, uniform, fairly heavy, and inert -- like gold beads. I see garnet is available -- is that special in some way? I found a 10" diameter mixing bowl in a garage sale for $0.25 a while back which is perfect for measuring out the right amount of gravel to fill the bottom dome of my tanks.
Finally, most folks say to use "1/8in - 1/4in" gravel. I wondered exactly what that meant. (Yes, I do have too much time on my hands.) My first guess was the individual pieces of gravel were between 1/8" and 1/4" in some dimension or other, but that didn't seem very scientific, and measuring a bucket load of gravel would be tedious (although, believe it or not, they use lasers and digital imaging to do just that these days). But Googling eventually led me to "Sieve Analysis", which is probably what's really going on. (This is a Civil Engineering discipline. As an EE, I find it suspect from the get-go.) If so, the 1/8" - 1/4" size means that if you've got a bucket of gravel, and sift it through a 1/4" screen, and then sift the result through a 1/8" screen, you will be left with "1/4in - 1/8in" gravel on the top of the 1/8" screen, and can throw everything else away.