I have funnels. They usually have grime, or left over brake fluid in them. When I need a clean funnel that won’t contaminate whatever I need to pour, this is what I do.I’ve see people curl up a whole paper plate to use as a funnel, but you are limited to a pretty tall, and narrow shape. This takes a second longer and will allow you to get a wide mouth funnel, with a variable sized spout.
Take a ordinary paper plate and cut to the middle of the it.
Overlap the two sides that you cut. Pull them further around to adjust to the size mouth you want on the funnel.
Tape it. Tape it on the inside as well if you want to double up the waterproofing.
Fold it flat and cut the tip of the cone to the desired size. Now pour with a clean new disposable funnel.