On my 6.2 stock fuel filter there is a small hose running from the bottom of the filter where the water would (hopefully not) collect, and this line runs to a small valve you can open and close by turning a small T shaped valve, and it is mounted right where the thermostat is, then there is a hose that drains down under the vehicle.
Is this a standard type of set up? Is the idea that if you were to get water in the bottom of the filter and the "water in fuel" sensor lit up on the dash, then all you would have to do is open this valve and the water would drain out?
I tried doing this once just to see if there was any water down there and i didn't see anything come out under the truck; but later that day i found some fuel had spilled into the valley of the engine and i am not sure why.
Can anyone explain if i have the right idea about this drain valve here?
Reason i ask is i am about to start running some biodiesel i made at home and ran through a water wash as many others do, and i want to be sure that if any of the water went through the line i could catch it before it is too late.
thanks,
Paul

How about adding a signature so it can help us with the year of your vehicle. What year is your vehicle? Military or Civilian?;)

It is a 1987 P-30 postal truck (walk in step van) with 6.5 n/a replacement engine.
Mainly i am just trying to figure out how to check the water collector - it has the stock 6.2 filter/seperator - and how to drain it regularly.
thanks again,
Paul

Square filter or round?

it's the rectangular box-shaped one which is held in place by the two wire brackets.
Paul

The standard box style filter housing has a plasic valve on the bottom of the filter housing. Yours might have a remote valve due to it's location. This is the water drain valve. If yours doesn't flow, I would remove line and check for restrictions. I like to drain these into a glass container and then check to see if water is present.:)