Without a seal or glue, you can't make two-object prints watertight.
A face seal is a compressible item that gets put under pressure and as a result, prevents the fluid from creeping through crevices. Rubber o-rings are a typical seal of this type, as are gaskets, but so is rubber (tube or string) in a dedicated indention or a gasket. Another type would be a Gland aka stuffing box or grease grove, which is then stuffed with a sealant - this could be string, hair, grease, or any type of other flexible material that reduces flow through by adhering to both sides and staying in the groove. With some designs, the gland can be packed with a fluid or viscous sealant after closing the item into its final position, for example by use of a syringe through a hole or a grease gun through a nipple.
Note that each of these designs has maximum pressures it can hold against.
A Labyrinth seal is a variant of a face seal, where two parts seal against one another by having many interlocking surfaces. A screw is pretty much a labyrinth seal. Most labyrinth seals are also packed with a sealant and, if around a spinning shaft, made from 2 halves that have a face seal against one another but only the (grease packed) labyrinth seal to the shaft.
A permanent sealant is a subtype of a sealant that can't be removed after installation. Some sealants in glands are permanent. The most common type of permanent sealant is glue. To pack them into the sealant gland from the outside, a syringe would be the best way. Depending on the pressure expected and the curing time of the sealant, just having a set of interlocking shallow grooves can be enough. Those then are coated before pressing the two halves together. The volume of the sealant needs to be taken into account in the design!