i've never bought from that specific site before.

but i ordered a pipe from a czech site a couple weeks ago, it arrived in a plain white box that said "GLASSWARE" or something like that very plainly on the box, i also had to sign for the package to receive it, sorta annoyed me but i played it off.

i don't see why customs would care, though. a water-pipe itself isn't illegal and isn't marijuana paraphernalia until you smoke out of it/associate it with pot.