Don't use N+ brand, they are bad for gunking up, I always had success with the generics but these days if I am going to CWE (rare if ever) I tend to go for pills formulated with paracetamol over ibuprofen.
You could use 2.5-3mL per tablet if 2mL is leaving you with a gunky solution that is hard to filter. If you are only using 30 tabs I would reccomend 3mL per tablet, or 90mL, rounding up to 100 probably wouldn't hurt any either. I find I need to use a higher amount of mL's per tablet if I do a smaller extraction, where extractions of larger amounts it is easier to get away with 2-2.5mLs.
There is no need for you to crush the tablets, if you put the tablets in a glass, pour the amount of lukewarm water you intend to dissolve them into over them, let them sit for 5 minutes and then give them a good stir they should dissolve pretty easily.
I always got the best results by using a cut out piece of t-shirt as a sort of preliminary filter before letting the solution drip through coffee filters, the reason for this is that you basically separate a large part of the solid matter from the solution before putting it into the fine coffee filters, dramatically reducing the likelihood of you clogging the filter up. I used to cut a square out of an old t-shirt, about the size of a handkerchief I guess, just like with coffee filters it pays to pre wet this so it doesn't absorb any of your codeine solution, make a pouch in the top of a glass with this and hold it on with an elastic band or something, pour the solution of water with the codeine containing pills into this pouch and let it sit for a few minutes, remove the elastic band and pick up the pouch, bringing the edges together at the top to close it up, squeeze this gently to get as much solution to pass through into the glass below without squeezing so hard to force the gunk through the material. This solution is not safe to drink, but it should now pass through your pre wetted doubled up coffee filters a lot easier than before, after which it is safe to drink and should have you buzzing nicely.
