Uses one wide mouth funnel (look at the canning section of your big box store (WallyMart)) adapts it to fit inside a Karter flask, for adding DME or yeast (no HOT liquids) !!!!

I added a label to keep track of them.

The OpenSCAD (free) file uses variable X2 to set the OUTER diameter that goes into the flask. If you need a different size, simple measure the INNER diameter of your flask, round down to the nearest whole millimeter, and change the X2 variable. Hit F6 to render and then ‘FILE’, ‘EXPORT’, ‘EXPORT AS STL’