This is one of three projects designed to reuse most of a discarded PET bottle.  The others may be found at the following links:

GIFT BOX KIT

CANISTER KIT

TINY FUNNEL ADAPTERS - DESCRIPTION

These tiny funnels are easy to print and will fit standard PET threads to create emergency funnels.  Each feature a small rib to provide an external vent.

There's no need to store a full sized funnel any more, with these aboard you can repurpose any water or soda bottle to a higher purpose.  Perhaps I should make a key-ring tab!

NOTE these won't work very well as nozzles on an uncut bottle, but if you cut the bottom out of the bottle or even puncture it they will make a very efficient funnel.

Print in anything you like, but to keep the threads nicely fitting perhaps no bigger than 0.2mm layer height is wise!   These are printed in PETG (Blue) and PLA (yellow) with a 0.4 nozzle and 0.2mm layer height.  No support is necessary.