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Get a profiling tool, they’re less than a tenner and will change your silicone life.
This. I got a set similar to the one below from Yorkshire Trading Co a few years ago for about £2. Done loads of sealing with it since and it just makes it so much easier and consistent. No faffing with masking tapes or licking fingers. Spray it with plenty of soapy water and away you go.
In terms of the OP, I have a fear of electrical work. I don't like that I can't see the electricity so I won't know if it's wrong until it's on fire. Plumbing on the other hand I have no problem with, it's just logic and you can see if it's worked or not. Apart from basin wastes, they can piss right off.