your inlet is behind the wall but your spray bar or outlet needs to have an opening otherwise you will have no circulation at all. I can't post a picture right now since the background is installed in my brother's tank, but I'll try too post one sometime this week, or just google it there are several instructions out there. I believe that we got the instructions either from aqua terra or the e-bay seller. I have never seen one with a HOB
filter so I don't know how that would work since the background are pretty wide specially the malawi one.