I just brewed a trappist style ale and I am ready to bottle it. I am a meticulous sanitizer. Just a question though. I have always filled my buckets/carboys with 5 gallons of star sans solution to sanitize it, and since I don't have the space I would dump the solution afterwards. This is wasteful and costly, so due to a response from another question I posted here, I was planning of mixing 1 gallon of solution and thoroughly shaking it in the bottling bucket to sanitize it. Is it a bad idea to try this sanitation method on bottles I plan to age for a good while (like a 18 months)?
What you propose will work fine. You can even keep StarSan in a spray bottle (mixed with distilled water it will last months or more) and spray down the surfaces. Although due to FDA regulations they have to list a longer contact time, Charlie Talley of 5 Star Chemical, makers of StarSan, has said that their tests show a 99.9% effectiveness after a 30 second contact time. Remember, that means simply wetting the surface, not full immersion. I usually only mix 2.5 gallons at a time for sanitizing 5-7 gal. fermenters. I could get by with less, but old habits die hard.
This is what I do regularly for bottling. Start with clean bottles, fill (let's say) 3 bottles with starsan. After getting everything else ready to go, I'll start a pipeline: empty bottle 1 through a funnel into (new) bottle 4, then fill the just-emptied bottle 1 while emptying bottle 2 into bottle 5. Cap bottle 1. Start filling bottle 2 while transferring starsan from bottle 3 into bottle 6… and so on down the line.
In the past I've generally done what the other answers here recommend: fill a bottle with Star San and pour from bottle to bottle. Works well except that it tends to foam up, making it more difficult to pour out. (But don't fear the foam!) I've also used a spray bottle, which is less foamy.
Recently I bought a Vinator bottle rinser, which is quick and easy to use. Takes less than a cup of fluid and does a good job of spraying down the interior. The manufacturer's bottle tree is not required. http://www.northernbrewer.com/shop/vinator-bottle-rinser.html
Finally, you can also consider sanitizing glass bottles in your oven. Winter is coming in the northern hemisphere, so here's a good excuse to heat up the kitchen. http://www.howtobrew.com/section1/chapter2-2-3.html
As Galapagos Jim mentions, the Vinator is AWESOME!!! I find it really reduces the consumption of StarSan solution and makes bottle cleaning a breeze. The tree is great too.
To your question, as others have mentioned, I only ever mix maybe 1-2 gallons and use a spray bottle to throughly clean the equipment, countertops, my own hands, etc. and I fill the carboy with it and shake shake shake. I fill my airlocks with it too.