Actually Matt and excuzzzeme, I had to take the pump off so I could fit a clamp on the barb of the pump, to stop it from leaking, and it did make a pretty big mess. Thankfully I only have to open the canister every 4-6 weeks, or more, I re-arranged the media stacking so that the bio-media is last. Floss is great but if'n it gets to the barb, its clogs for some reason. I went about 4 weeks last time. As to address the mess issue, I have a hole that I put a piece of tubing in for CO2 ingestion in the intake. If'n I need to open the filter I just drain enough so that hole is above the water line to break the suction, then at the WC valve, blow until most of the water is pushed back into the tank. Put a catch pan below the filter, and just remove the filter. Not easy but it does work, and seeing as how I won't need to get into the filter all that often, I'm not changing it.
Bob: No, Pentair Aquatics does not suggest anything about a vertical mounting, but pump doesn't mind one bit, and it is indeed dead silent this way. Heck, my eclipse 5 filter is louder than that thing, I'm spoiled, lol. I think it rivals sound levels with the Renas and Ehiems. I don't have a DB meter, but I can't hear it over the two computers in the same room.
MG, Currently holds a lot of media
Current stacking (in order
3 AC 70 foam pads (trimmed to fit)
6 layers of Rena XP 30PPI (cut up and trimmed to fit)
bag of crushed coral
2"-3" of floss thats been stuffed in there
2 pot scrubbies
I don't recommend this canister on larger tanks, 10-30g though, its perfect. If you can get something in about 4 1/2" diameter or larger when getting into the bigger tanks.
Stinker, That would be kind of throw-away canisters, due to the small opening, not practical. Although it might work for something like a bio filter (add lots of gravel) and might work also as a nitrate factory (not exactly a good thing)