Type of bulkhead (wet side + dry side) - threaded + threaded; threaded + slip or slip

[byee]

Here's a quick photo of how I was going to use the O-ring by placing it between the bulkhead and the MPT x SLIP.

[gregzz4]

That o-ring isn't needed

That's your standpipe for a drain correct ?
Just wanted to make sure you're putting the bulkhead gasket inside the overflow and not on the outside of the tank
And the nut goes outside the tank