Waterproofing a temperature sensor
I tend to coat the entire assembly in hot melt glue, and put a sleeve of heat shrink over it. On gentle heating, the sleeve shrinks, extruding the glue out of the ends, minimising the bulk of glue around the assembly, and sealing round the wires. This way, the bulk of the waterproofing is provided by the heatshrink tube, with the glue sealing the ends. Squeezing the ends down further reduces the cross sectional area of glue exposed to the fluid.

Note that stranded PVC sleeved wire is not waterproof between the insulation and the wire. The insulation should come all the way out to the dry area.

If the assembly needs only two connections, then I often use co-ax so that there's only one seal being made.