Here's a tutorial I've dug up that I think I've posted here before. Works pretty decent depending on how you do your lines.
Sorry for the long stretch, but its a good tutorial. Principles apply to Photoshop, disregard the fact its a Sai tutorial.
Alright, i'll check that out, thanks
In the meantime, this is the best i could get


It's only slightly thinner than using the 4 pixel brush, but it's something at least, and it properly fills in outlines!

There is still that mess of scattered opaque pixels along the edges though, but they only seem to appear where the outline is mostly opaque, so this will have to do