The original question was how to service and lube a thru-hull with the boat in the water.  What would happen if you took out the four screws on the inside part of the thru-hull? Warren’s response was something I’d never heard before.  The thru-hull comes with a plug that can be used to plug up the thru-hull from the outside.

From post by Warren Elliott:

For disassembly while afloat (those 4 screws), there is a small “plug” extending out from the center of the handle.  Pull this out (which reveals the handle’s securing screw)…..it is made to fit snugly in the fitting from the outside of the boat, thus avoiding a gusher. (This does require a slight bit of swimming!).

An additional feature of that plug is its closed circle handle; tie a several foot long string to that handle, securing the other end to a lifeline. Then, when the