For solid nozzles, resin printing would be sufficient. The result is smooth and non-porous enough.
For silicone inflatables though, no manufacturing technique available in the DIY space today offers much of an advantage.
Closest thing to useful would be 3d-printing a mold which can be used to shape a sacrificial material (eg wax) into the shape of the internal cavities of the nozzle. This would allow casting the entire inflatable in one piece.
While this should help avoid any sharp edges, cracks, and improve durability, it's important to note that the existing designs (Klystra, CleanStream, the SiliconeNozzles.com Single Balloon) used silicone of different hardness, essentially different materials, for the balloon and the tube. Replicating these designs 1:1 with a single hardness may not be useful, producing either a tube that kinks and collapses or balloons that neither be inflated to a smooth spherical shape nor collapsed flat enough to allow easy insertion.
Some silicone SLA printing exists already, but that uses harder silicones, and may not produce the glossy finish required for a hygienic reusable product:
https://formlabs.com/eu/blog/silicone-3d-printing/
Finally, producing something like the coloclean and other medtech3000 products with a resin printer, where the balloon membrane is added in post-production is definitely possible, and should definitely be explored. A larger-bore coloclean is sorely needed by the community. The challenge here is securely and hygienically bonding the balloon to the tube. I'd love to hear some ideas of adhesives and seals that could be used.