One A&P works for a jump school - the planes fly all day, up & down. Another works for a flight school - ditto with the added plus that students sump between flights. Primary training students usually fly in one hour increments, mostly touch & goes. During a long summer day a single plane will rotate thru 10+ students & burn 50-75 gallons, being sump'd 10 times, pulling about 4-8 ounces per tank per plane. Some pilots only pull a few ounces per tank. On a Cessna 152, I'll pull 6 ounces or so from each wing tank, then about a quart from the gascolator, then re-do the wing tanks (about a half gallon total). In humid climates you may have to pull off more to be sure you got all the water out of the fuel. Spring brings another opportunity. Since lots of light singles use Mogas (autogas w/o alcohol) and it tends to deteriorate with winter storage, they need their tanks drained before resuming flying in the summer. 'Spent gas' mixes well with other alternative fuels for diesel use. Don't use too much in the blend or you will wreck the injection system.