Update 02/2024:

I made a WDT-Tool and cup which uses my previously designed funnel as a guide. It consists of two parts, a needle plate and the main body. You need 28 pins (25mm max. length, 3mm pin heads) to insert into the needle plate. Then let it slide into the main body and lock it in with a big flat screwdriver. The cup is mainly to cover up the needles when not in use.

Print the body and funnel upside down and the rest as it is.

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Many funnels I found are made to sit on top of the coffee container and get their stability by a outer ring that sits flush against the perimeter the water container. I use a jar for the ground coffee with a holding pin in the lid for the coffee container. So the other funnels won't stay securely on top as the wider perimeteter of the watercontainer is missing.

This funnel sits on top and, with a thin wall, inside of the coffee container. It ensures stability just with the container itself.

Print upside down, no supports needed. Use brim if unsure about bed adhesion, for me it held good without.