defuelling can happen with airliners, where there are strict rules about reusing the defuelled product ONLY in the same company's aircraft - all to do with Cladisporium Resinae, a bug that loves Jet A-1.
In my aircraft, I often syphon 20 or 40 litres off into one or two jerry-cans to bring the AUW down into the aerobatic envelope if taking someone for a ride.
Kit required, clean length of hose (Avgas compatible, such as B&Q garden hose), one or two jerry-cans and an ability to suck hard on the hose! I let my g/f do this.
Not a silly question, at all.
Stik