What's a pugmill ?

Pretty much, yes.

You don't need one - not unless you need to recycle huge quantities of clay (or small quantities but you've got a load of money to spare!).

You can buy clay "ready made" and more-or-less ready to use. You can also buy it dry and make it up, saves paying to ship water around the country, but I imagine the process of reconstituting it and letting it mature is pretty laborious and time-consuming. I don't know if anyone actually does that (and I know my local colleges don't even for the volumes they use)and I don't even know if all types of clay cab be bought dry, so I guess I'd better shut up now.