Solvent as glue:
There are some solvents (thinners if you like) which causes the polystyrene (or simply styrene) in plastic kits to go soft.
If this happens between two mating surfaces the plastic (styrene) will go soft (the binding between polymer chains is temporarily broken or loosened). After a short while the solvent evaporates and the polymer chains start to bind harder to each other again. This results in bonding across between the two parts.
Using tube glue: Smear glue on one surface, press the other surface into the glue, let dry and remove the excess glue.
Using liquid glue: Use a small brush to apply glue on one surface, press together, let dry.
Using solvent (or call it liquid glue without any solid content): Hold the parts together, apply a small amount of solvent to the joint, hold the parts together for a minute or so. Let it dry completely.
The advantage with using a solvent is that there is no residue outside the joint. It is possible to go directly from dry-fit to glued and finished without changing the position of the parts.
The dangers are spilled solvent, a kit can be wrecked in seconds. Another danger lies in the big advantage: the capillary action
this will suck the solvent into the small gap between the two parts BUT it will also draw the solvent into the channels caused by your fingerprint. If you happen to hold a finger or thumb across the joint when applying the solvent the result will be a 3D-fingerprint on the surface of the plastic/kit.
The easiest and cheapest wat to get hold of a usable solvent is nail polish remover. If it has a content list you look for ethylic acetate. If it doesn't you can test it with a pice of styrene. A small drop on your thumb and press the thumb onto the styrene. Get a quick fingerprint? Yes = good stuff.
No or only a faint print = useless.
Nail polish removers are either with acetone or acetone free and you are looking for the acetone free stuff.
The method is easy to learn, easier than using tube glue.