If you have an old greensmoke or blu cart they both have extended pos pins in them and they can be modded and used as a bottom feed pin. The vivi nova pin too, its hella long but will need modding to smooth down the bridged air channels..
The two smaller pins are from a greensmoke and a blu carts they have been cut so they are 5mm longer uncut, I used them for a test unit works great. The pin on right is a vivi nova pin it is 5mm longer than the uncut blu and green pins. Nice pins for mods in those carts..
Look for Mamu's OKR build she uses a finishing washer for a catch cup, she doesnt bottom feed but utilizes a catch cup for atty leaks. I do not know the right size finishing washer so look for her tutorial.. Or Post and ask her..