Hmmm that's a good idea!You might want to cut the tops off of the bottles slightly below the water line of the sump to allow the sump water to drift over the surface of your DSB bottles, or maybe use the entirety of that milk jug for your removable DSB. giving you a lot more surface area. Also you should make sure any holes in the sides of the bottles are not in the bottom half, as that will allow oxygen exchange down at the bottom, preventing anaerobic conditions.
Cutting the bottles I mean. I want to keep the three separate containers so I can remove one and replace the sand each year. The idea being keeping 2/3 of the bacteria and never running into a dsb crash (even though these are probably too small to cause too many problems)
Yes the holes are all just below the waterline.