How much fuel is left behind after siphon?

[Laser145]

Drained the tank on my 86 Osprey 170 using a siphon through the motor fuel hose. hooked up a hose after the primer bulb, ran it through the scupper and kept it lower than the tank itself. pumped the primer, and let it go.

My question: How much fuel is left over in the tank? Where is the pickup?

Can I simply top off the tank now with 20-something gallons of fresh pre mix and run it? The gas inside the tank was a few years old.

Thanks

[dbiscayne]

pickup is supposed to be mounted near the rear of the tank, but how close the pickup tube gets to the bottom of the tank (1/2 inch???) would just be a guess unless you want to remove and measure the length of the tube & compare with the depth of the tank.
If you've got a half inch of old fuel left in a typical 30 gal capacity tank you've probably got under 2 gal of old fuel in there. Should be OK if you're gonna dilute it with over 20 gal of fresh gas.
Did the old fuel have ethanol in it? Are your fuel hoses rated to handle ethanol? Plenty of old fuel lines have collapsed from the inside without much evidence of failure on the outside. Might want to replace the water separator filter & the under cowling filter an extra time or two.
If there was water in the old fuel you probably siphoned most of that out since you were pulling from the bottom of the tank.

[KB4ET]

I recently drained my tank the same as you did, I used an elect. fuel pump and connected at the point where the fuel line attaches to the water separator filter. After I was satisfied that no more fuel would come out I then filled the tank, which is a 49 gal. tank - it held 48.6 gal. Fuel capacities can vary a little with the density of the fuel, but apparently, this method will get most of it out.