Sketchup is a mesh modeler; it keeps track of the surfaces of objects. It's great for things like planning woodworking projects or mocking up some architecture, but when you hand the results off to be 3D printed, the meshes never end up aligned just right and you got holes and glitchy models. That is not to say you can't do amazing work in Sketchup, but that's entirely due to the skill and dedication of the person behind it. Sketchup is certainly doing him or her no favors.
OpenSCAD and other modelers intended for CAD are solid modelers. "Solid modeling is distinguished from related areas of geometric modeling and computer graphics by its emphasis on physical fidelity." https://en.wikipedia.org/wiki/Solid_modeling
Once you have an object in a CAD program, the resulting STL output should be well behaved and suitable for 3D printing.
There are several programs available that exist solely for the purpose of taking the output of programs like Sketchup and fixing up any issues, so it is possible to use it for 3D printing, and indeed it is very popular on Thingiverse. Dedicated CAD programs have a whole host of tools beyond what Sketchup provides that make them more suitable for creating manufacturable objects, though.
OpenSCAD is an acquired taste, and requires some facility with programming. If you're comfortable with Sketchup and want to check out a true CAD program, I recommend checking out Autodesk Fusion 360 or OnShape; both have powerful free tiers available. DesignSpark Mechanical and Autodesk 123D Design are both a bit easier to pick up, but also both more limited in certain ways.