So far, so good....

Got 5 gal out of a BE-18T nacelle tank once, though was before the change to KingAir-style fuel caps.

The operation I work for sumps the tanks on the preflight if the airplane flew on the previous shift. So it is preflighted by a new crew twice a day. If it sits for more than a few days we usually sump again. We have mechanics on site or a phone call away so the leaking sump isn't an issue for long.

FWIW the instructor teaching the class in my initial B200 training actually said that sumping was a maintenence function only, citing that turbine engines are not susceptible to water like recips. Yeah right

Not entirely accurate. "Checking fuel" for contamination and sump draining are maintenance functions at the major airlines.

I was a Line Maintenance Crew Chief for a major airline for 20+ years and one of the things we did on each line check (overnight checks) was to sump the aircraft fuel tanks. We did this early in the morning after the aircraft had been parked all night. I had our crew do it just prior to the fuel truck showing up to allow maximum time for settlement.

And yes, I did it on the 747, DC-10, 727, 757, A-319/320, etc..

It was not uncommon to get a gallon or more water out of each tank (especially the 747's). And yes, I have seen a sump drain get stuck open and dump thousands of pounds of fuel on the ramp. It was usually something like a rivet or small chunk of sealant that was the cause. Some FOD left over from the last HMV with tank repairs and a poor cleanup job.

Revisit that statement in ten years and see if you still thin the same.

Some additional tidbits...

• Water does not weigh about 9# per gallon. Fresh water weighs more in the range of 8.3 > 8.35 PPG.
• Water settles through Avgas at a rate of Apprx. 15 Min. per vertical foot. It takes much longer with Kerosene/Jet A, Etc.
• If sumping a Kerosene burner, and are having trouble telling water from fuel; you can pour some fuel on a piece of paper. When the paper dries the fuel will leave a noticable stain.
• The primary reason for shaking the wings is to dislodge water that may be puddled in various parts of the tank floor so as to have it flow to a low point drain. This is sometimes an issue with bladder tanks and can be an issue with an aircraft parked at a severe enough angle.
• I too have had a couple incidents incidents of large amounts of water in the fuel as well, bad fuel caps. I also have had water find its way into the static system. Be sure to check the static system drains for water as well...

On thing to consider is microbial growth in jet fuel, namely if planes that fly once a week or less. Any time my king air flies after sitting for a week or two I notice that It often develops several ounces of red algae along with water contamination.

Keep in mind that a pt6 would probably burn a gallon of water without an issue, but when you set takeoff power it's nice to have the piece of mind that you got all the junk out.