Use this cap and a bit of 4mm PTFE tubing to turn any common PET pop bottle into a squeeze-to-squirt “lab bottle”.

Prints without support in any rigid material. Either cut the washer out of an old inner tube, rubber sheet or print in FLEX. I used a tiny bit of epoxy/glue to seal the PTFE, just put a tiny bit of adhesive on the outside of the end of the PTFE and jam in the hole. Epoxy won't stick to the teflon tube (almost nothing does) but it does cause a good enough seal so you don't get air in the stream. You might find it seals well enough without the adhesive.

8.5 in or 215 mm of PTFE tube will fit a 20oz pop bottle pretty well.

Good luck and please post your makes.