Refill bottles rarely fit on their counterparts, you have to hold them by hand all the time. Creamy fluids like laundry detergents can take a long time, a boring process. Enter the customizable bottle adapter. With its integrated funnel, nothing drips along the adapter and outside the bottle, and everything is kept clean.Check the resulting STL, with reasonable parameters there should be no need for support structures. The inset parameter must be just large enough to leave room for the wall of the lower bottle. Adjust with the heights of the cones (inner and outer) to minimze overhang angle.