so what happens to you after you go to leviathan?

As Pinhead said, they're demons to some and angels to others, so there have been some who enjoyed what they got. Frank might have too, but the prospect of an unending mixture of pleasure and pain for eternity was probably overwhelming for him, which is why he wanted to escape. I believe a few who started out like Frank, only as human "victims" trapped in a personal Hell, can eventually evolve into cenobites, while some people become cenobites instantly, as in Channard and Pinhead.

However, I doubt everyone becomes a cenobite eventually. While some people might enjoy their experiences at the hands of the cenobites, that doesn't necessarily mean they're cut out to inflict it on others.

I just assumed the cenobites get all the pleasure from torturing the victims.

I think it depends on if Leviathan senses something in you, like a deep carnal desire. For instance Capt Spencer, the nun, the child, and Dr Channard all seemed to instantly changed upon admission, where as Frank, Julia, and Christy were left to their own devices.

Perhaps the hierarchy is two tiered. The Cenobites become the legion soldiers of hell, and those unchanged become denizens of the realm who experience hellish pleasure and heavenly torment for eternity. Julia for example seemed to delight in the realm so much that she became accustomed to the world and claimed some nonexistent power therein. Frank who seemed fit for that world suffered due to the constant sexual excitement it promised but took away as soon as he came close to it.

I'm just making this up off the top of my head, so it could be way off.