What is a "Solid Tank Joint" in reference to bongs?

Hey everyone, I am in the market for a decent sized bong - and I have narrowed it down to 2.

http://www.everyonedoesit.com/online_headshop/GSPOT_Cylinder_Straightt_with_Ice_Piercings.cfm?iProductID=4058

http://www.everyonedoesit.com/online_headshop/EHLE_Glass__5mm_Ice_Cylinder_Bong__45cm.cfm?iProductID=5923

What does "solid tank joint" mean in regards to the first bong? Does this mean I am unable to replace the downpipe with a diffuser? Sorry, a bit confused here...

you see wh ere thedownstem goes in?

basically you can't pull it out now because it's sorrounded in glass, that's waht they mean by solid tank joint..

so I would not be able to put a diffuser on this?

nope, its sealed in glass.

if you got a bit of money and want a diffuser get a toro