I do whatever is convenient; usually the spray bottle is impossible to find, but my bucket of StarSan is hard to miss. If I spray, I dump the rinsate down the drain. If I put in a “bunch,” I’ll pour the rinsate back into my StarSan bucket.
This is me as well. For the most part, I only use a bucket for bottling. When I’m done, I fill it with PBW or oxyclean and soak it along with all my other implements. Then I store it in a new trashbag to keep it dust free til next use. For sanitizing, I fill it with enough starsan to completely cover the spigot opening. then I swirl it around a bit and coat as much as I can. I’m a bit of a klutz and I tend to spill if I swirl too much so I just spray the top part of the bucket liberally, It all gets drained back into my starsan bottle in the end. 
I used to swish.
Make sure it’s clean first.
When needed use a clean surgical sponge (soft cheese cloth) to topically apply starsan to the interior of both lid and bucket. Drain out excess.
Done.