That's a nice piece. Its a 14 mm what is often called a Dewar type joint. You will need a 14 mm male to 18 mm female adapter if you want to use the 18 mm Epic GonG. But I'm pretty sure they also make the GonG in 14 mm. In any case, when you start using glass you will end up collecting a bunch of adapters as you go.
With regard to cleaning, read this thread on PBW...its the right stuff:
http://fuckcombustion.com/threads/pbw-the-chemistry-of-clean.7854/
Wrt to what glass and what sources to use on DHgate, I suggest that
@mrbonsai420 is a GREAT source of info as are others here. I have not yet bought from DHgate but will be ordering a D020 from Steven, I believe, shortly (just because). But Bonsai has a lot of experience with these suppliers and can probably give you a good steer.
As far as
@ataxian helping you out also, yes....he's sometimes a bit cryptic in his language but he often has a very unusual and interesting perspective on things, is well worth reading his posts (well, most of them LOL) and he is a most beloved and experienced member of FC. Eh...them surfer dudes...I never could understand what the hell they were talking about anyway!
Cheers