Will depend on the quality of the silicone. I have found that good quality silicone does not retain odour. Rinse with warm water and air dry is sufficient.
Poor quality silicone, nothing works! It will retain the odour of your e-
juice and everything else you use to try and get rid of that odour. Over time the odour does diminish, but I do not have a time frame on that. Too many variables. If using a proprietary design squonk bottle that can not be replaced by something of better quality, I would suggest purchasing multiples of said bottle.
There are claims on the interwebz that a squeeze test can be used to verify the quality of the silicone, or at least verify if fillers are being used. They state by squeezing your silicone, if it changes white, fillers are used. I do not know how much fact there is to this, could be marketing BS, but do know out of all my squonk bottles, the ones that retain odour are the same ones that turn white from a squeeze test.