Plumber taught me a trick with sealant back in 2006/7 when we bought and renovated where we now live ... basically use the sealant gun down the line of what you want to seal then get some Fairy Liquid (other brands are available) put some on a finger and just run it down the sealant line - any excess at the end just wipe off your finger with a cleaning wipe... works a treat and leaves a lovely smooth sealant line ...
I use frog tape to mask off where the sealant is going. Whip the tape off once you have gone over with a soapy finger to push it in the gap. Gives a very neat finish. Remember if you are sealing around a bath to fill the bath with water before doing the sealant. If you don't then when you do fill it the bath will drop down a bit with the weight of the water and rip the seal.
I’ve always used one of these rather than my finger. The top part is made from some kind of silicon material so it doesn’t stick to it.
I used to do my own years ago and would spend ages putting masking tape on either side of where I wanted the sealant and used various tools for smoothing it out. At the start of lockdown I had a couple of houses I was renovating and needed to silicone the bathroom and kitchen in both, so decided to use a fella that a mate of mine (plumber) uses when he does bathroom refurbs. He charged me a couple of hundred to do both kitchens and both bathrooms and he had a range of colours in the back of his van that I never knew existed! The kitchen and bathroom are probably the most expensive rooms to renovate and after spend a few grand doing them, the 200 quid was money well spent for the professional finish achieved.
It was a proper head ****, hence the beer! I got no help and my hands and arms were too big to get down some of the gaps and bolt the **** up. Did it though, but was at it till gone nine last night.
When we had the bathroom done last year, she bought some stuff from the John Pye auctions. We ended up with two baths tubs and two shower closets and a spare sink I think. This bath wasn't any cop, but because it's on line auction you're stuck with it. Been in the garden ever since. Sold the rest of the other stuff.