You don't remove it, mate. If you're trying to clean the Le Brea Tar pits out of the bottom of your case, just put the side-covers back onto the lower part and fill it with solvent. By the time the fluid-level reaches the throwout-rod hole it's already completely submersed the sludge.
Leave a drip-pan under the case as I really doubt you're going to get a tight seal. You only need to put on the left-side and stator cover as well as the right-side cover. Three pieces plus the oil plug, of course.
Um, well that's how I do it anyway since I can't afford to fill something with enough solvent to completely submerge the cases inside and out.
Works a treat.