This is my homemade sub tank. Dirty I know, but it has been on the shelf since I bought my 70 degree tank.
I installed a 90 degree 1/8" MxM NPT elbow at a low point. I was thinking of doing it on the lowest tab to the right but realized that I can never use that fuel anyway so I let whatever debris and gunk collect down there.
I also installed a nipple with 1/8" NPT threads up top. I regret that I didn't install a 90 degree nipple and I wont change it out as it hold fuel. Don't fix what's not broken...
The way I did it was to drill holes a bit smaller than the 1/8" threads. Then I heated up the plastic a bit with a heat gun. I did it until the edge got a bit rounded off but the plastic was still quite rigid. Then I screwed in my elbow and nipple and let the plastic cool off. I also put some glue around the elbow as you can see (white gunk), but that didn't stick to the fat plastic so that was unnecessary. It will hold anyway. I then used a short fuel hose and a quick connection with hose clamps.
As I had the safari tanks I hooked it in to their hook-up point, but if you don't I guess you have to install a nipple at the bottom of the fuel pump housing to connect to. It's tricky to get the fuel hose routing good around the shock and it's not much space to work with, but it's possible.
My tanks weak point were at the very back up top. I never managed to seal them 100% so when the tank was full it was sweating out fuel. Not much but it was constantly wet until the level went down. The material was very thin and I tried to mold it using a soldering pen. Too much and the plastic turns grainy and is burned... I also tried different plastic paddings and what not with no success. This plastic is quite special. When they mold the tanks they throw in a free radical that connects all plastic molecules into one big chain. That's why the tanks are so durable. You could say the tank are one big molecule. So when you crash and bump it it will slowly go back to it's true form as that's the way the molecule was made. It's very good, until you try to fix it with glue or heat. Then it will not cooperate...
I did however manage to seal the two places where the metal inserts are! I very carefully smeared the plastics around the metal and managed to seal both!! But that was fairly easy due to much more material and less surface.
Before you install nipples and what not fill it up with some fuel and see where it leaks. Try to fix those leaks first. If you're not happy with the result plug the holes and use it as a normal frame. If you are happy you can start to convert it.