I have limited wall space since I like to keep the tank close to the wall. I have played with HOB units and even tried to DIY a narrow one to fit behind my 3in gap. After spending more than I should have a messing around with HOB units, I finally decided to drill the tank and be done with it. The setup is a little weird but that is the fun of DIY.
I used a 1in bulkhead that feeds into a 1 1/4in U shaped train that has a T in the middle to feed the sump. This allows for a siphon to happen in 2 places if the flows get too high. The bulkhead will siphon into the U and the U will siphon into the sump if the water gets too high. I am not sure if it has any benefits but It allowed me to have the drain solidly supported. I use ping pong balls to cap off the pipes and keep the system quiet. I do not have an overflow box. I use 2 90's in the tank with a 3D printed strainer and I can control the level by adjusting the position of the strainer. It has been running for a few days and no problems.
I was nervous to drill the tank but it went really well.
I 3D printed a drilling guide and double sided taped in into the proper location. This guide also has a built in water dam to keep the drill lubricated. I drained the tank into a storage tub and got to work. I used the same tape in the inside (double sided speed tape) to keep shavings and the cutout in place. This tape is very durable and strong. I had ZERO chipout from drilling and the drill did not penetrate the tape. This allowed me to flush the shavings from the hole before removing the glass plug. I used a cordless drill at almost full speed and very light pressure.
I decided to paint the back of the tank this time also and remove the silly background. I installed the bulkhead FIRST backwards and then painted. This leaves me a clean glass surface for the gasket on the OUTSIDE of the tank. I glued the PVC while the paint dried and waited a few hours for it to cure. You can see the U shaped sump drain screwed into the stand and properly spaced with a couple of LEGO blocks lol.
This is the final configuration. The tank is nice and close to the wall. I still can get my hand behind it to remove the coupling and adjust the tank drain tube height that feeds the sump drain.
Overall the system works really good and I am glad that I finally drilled and stopped messing around. The system is silent aside from the water flowing in the pipes. It has a soothing fountain sound that is just loud enough to enjoy and not be obnoxious or distracting.