This bottle brush prints pretty easily (use exactly 0.2mm layers) but the tricky part is freeing the bristles from the outer support tube. To do that, I've created a separate shearing tool that you press inside the brush support tube to shear off the ends of the bristles.

I printed this in PLA which creates stiffer, but more brittle, bristles. PETG might be a better choice for using it to actually clean bottles. Also, make sure to use the “Random” seam alignment option so that the seams don't get aligned with the base of the bristles.

After printing, press the shear tool into the non-handle end of the brush support tube. Don't twist it - just press it slowly all the way down the length of the brush until all the bristles have been sheared off. It may help to tap the end of the shear tool with a small mallet.