In theory, it can be right next to the wall. The bowl may need to be propped up when changing out the solids bin/urine bottle. It may be a bit uncomfortable to sit with your back directly against the wall so you may want an inch or two off the wall. We recommend testing the location and comfortability before fastening it to the floor.

The vent housing can be swapped from either side to fit your space and the T-Bar for the vent hose swivels to ensure your unit can fit almost anywhere. 

You may also be in the right environment and build that external venting is not needed. Some will add a charcoal filter to their vent housing instead of using the vent hose.

But it boils down to what is right for you and your build. If you are unsure, you can contact us, and we can help you with any further questions and be able to help with a photo rendering of your space.