One thing I've never liked about HOB filters is that the intake is just under the outflow and it seems like water is just circulating in a small space. I decided to remedy that by moving the water intake way to the other side of the tank. I just cut up some 1 inch PVC pipes and used 3 elbows.
I also filled up the inside of the PVC pipes with some K1 media so that it would increase the filtration capacity. The HOB intake goes into the taller pipe. The taller pipe has to be higher than the level of the water so the water intake can only come from the other end. The other end can be any height as long as it's under the level of the water as well.
I just realized that if I made the other end higher, it will limit leakage from the tank if the HOB springs a leak.
The blue things seen at the ends are 1 inch bioballs that act as gates or grates that prevent the K1 from leaking out. The one at the far end also prevents fish from getting sucked in. I may put a big sponge over that as well for mechanical filtration.
This is such a simple device that I don't know if anyone has ever made anything like this before. If not, may I present the JohnHuff intake: