I made this 55 gallon drum fluted funnel for our waste coolant for my auto repair shop. I designed it so it does not hang over the edge and won't come into contact with anything that is right next to it. You will be able to have it directly against the wall as well. The flutes help with channeling the fluid down into the barrel. The funnel is threaded for a 2"-11.5 NPT thread.

The files with threads have already been reduced for filament thermal expansion. So you should be able to print this and thread it directly onto your barrel. The print in this photo was slightly on the smaller side and threaded in really easy.

NOTE: You may want to test just the thread part and make sure it threads ok on your barrel. If it's too small, just increase the X & Y by 0.5%. Same with the locking ring.

The screen had nubs on the sides that mesh into the flutes. If you want to make it 'splashless', trim down a large Scotch Brite pad. You can also buy splashless matte, but they are expensive and the Scotch brite works well too. To anchor it into the screen, use a plastic push nut or a screw that fits inside the screen holes.

If you're using chemicals, like oil, brake cleaner or gasoline, you're going to want to print this with a filament that is chemical resistant such as polycarbonate or PETG.

Print the funnel upside down with the large opening on the build plate. The screen is tapered on the edges, so make sure you print the top down to get better print quality on the edges, however I don't think it's that important.

NOTE - Australia, South America, Africa, etc... (south of the equator areas)
If you are in the southern hemisphere (south of the equator on this planet), you need to use the funnel and screen files labeled 'southern' at the end, so the flutes go in the correct direction for the spiral fluting.