Originally Posted by soapy_junk
that is the orig / ideal plan.. but what size hole is ideal for threading in the nipple?
I don't think it's important for the nipple to be able to 'thread' itself into the drum. With the larger diameter pipes you're working with I don't think you'll be able to properly thread the nipple because the drum is curved and more pronounced the larger you go.
If you're using a locknut it doesn't matter. The hole should be just large enough for the nipple to slip through. Just make sure to use an elbow that's threaded on the inside