Yeah I prefer to use a 25 g needle (I already have a couple of boxes, 23 g would be about the same) it does less damage to the septum of the HCG bottle than a big harpoon and allows me to easily add the BacWater in a gentle fashion as compared to a 31 g where you really have to take your time to keep it from coming out like a pressure washer.

PS I use the 5000 iu Corian HCG and also dilute with 2 mls bac water...as the "wise one" said....all hail MickeyKnox!!!!!