Where do i need to go to do this?
Just to add to and clarify IvoryOwl's stuff:
1. Go into Submission.
2. Explore the unaligned tunnels (ie. those not surrounding a fortress).
3. Find a Slime who wants to transform you into a Slime.
4. Win or don't. Either way, get transformed into a Slime. But leave this Slime in place regardless (they'll be an ongoing source of biojuice going forward).
5. Now enter the tunnels surrounding the fortresses and start fighting Imp patrols. This is also a great time to get the Orgasmic Level Drain Perk and get your MC up to level 50. Being a Slime really helps in the fights as you'll have 100 Physical shielding, but with the OLD Perk you only need to win for the loot as it's the fucking that levels you up.
6. Imp patrols always carry transformation potions (specifically, they are always carried by the second Imp). Ordinarily it's some bullshit futa stuff. If you come into contact with them as a Slime, however, the potion will be a Slime-to-Flesh potion. So pick those up while you're on your way to level 50. Aside from the potions, grab the weapons/jewlery/money of the leader; no other loot (it's worth bugger-all and doesn't stack well).
7. If you do this correctly, you will end up at level 50 with enough cash (after selling the loot) to start a dairy (after which money means nothing). You will also have a nice starting supply of unsliming potions and a steady source of biojuice for the transformation of yourself and your slaves.
8. Remember to go talk to Claire (at any of the Submission entrances) about what the Slime who transformed you said. You won't be able to do the Slime Queen quest until you do.