This is a cap fitting standard US 1L & 2L plastic soda bottles, meant to hold 4-5 Mentos™ candies to be dropped into bottle to create a rapid CO2 release (e.g., Mentos + Diet Coke soda fountain). It could easily be extended to hold more, but 4-5 was all we needed for the science experiment.

The quick release is operated by sliding a toothpick, coffee straw, nail, or similar through the holes in the side near the base, then stacking the candies (or other payload) onto it. When pulled out (directly or with an attached line) the contents of the chute will fall quickly into the main body of the bottle, since the chute size is almost the exact diameter of the bottle throat (nothing to get caught on).

There are 2 versions of the cap: the straight up "MentosCap" file is an open bore at the top. "MentosCap_Mk.IV" uses an interior parabolic compression to restrict the flow to a much smaller outlet at the top, and has been pre-inverted for easier printing. This requires filling it with mentos (and the quick-release) before attaching it to the container, but also yields a much higher spout (but watch out, because the compression means it also uses the quick-release holes as additional spouts out to the side!)

Tiko3D

Doesn't Matter

Doesn't Matter

0.2mm or smaller

Doesn't really matter

MentosCap may be easier to print by turning the model upside down for some printers. Depending on available resolution it may also need to be scaled up or down by 1-2% to the the right fit. MentosCap_Mk.IV has been pre-inverted, and should be printable without supports.

Make sure the interior threads are free of burrs and blobs, and try working it on and off a bottle a few times to help clean it up. After doing that it becomes much easier to fit, and should still maintain a nice snug fit during fountaining.

Remixed http://www.thingiverse.com/thing:1207893 via TinkerCad to remove the funnel bowl, hollow out the lid of the cap a little more, and add a tube extension.