How to drain old fuel

The tanks should have anti siphon valves on them and they seem to be working .

Your fuel pickups won't reach the bottom of your tank, so you'll never get all the water and gunk that way. Technique I've heard is to buy a cheap fuel pump at an auto supply store to pump it into containers. Drop the intake hose through the filler neck or through any fitting on the tank. There are weights made for putting on the end of suction hoses, might find them online.

There is a funnel with filter and water separator: Mr. Funnel. Some people pump fuel out and into the funnel, and let it run back into the tank. Eventually it is all filtered, clean, no transferring, and no disposal of questionable fuel.

I spent two days driving my smallish cruiser into pretty big waves getting it home, and pretty sure whatever gunk was in my tanks was sucked into my filters. Probably not good technique, but one less thing I need to worry about with my new used boat.

You might be surprised that even the biggest ship afloat can be caught out by dirty fuel and they have some pretty serious ways to clean out most of the gunge that a small one doesn't.

I doubt they and their fuel tanks get bounced around as much as mine did over those two days. I can only guess everything got mixed around pretty good. Many tanks of fresh fuel along with lots of sloshing. I'll be changing the filters in a week or two, interesting to see what is in them.

Airplanes I've flown get their tanks swabbed out occasionally. Big ships burn bunker fuel, filthy stuff, they must have a lot of ways to clean out their tanks. I've cleaned out car fuel tanks when changing fuel pumps, surprising all the junk I've found there.

W

You may want to hire or make up your own fuel "polishing" system to get it clean. Water will rest at the very bottom of the tank. Did you recently use a biocide? Where's all the gunge coming from?

Good points, I made the assumption it was diesel - it may be something else.

Fit a filter with an alarm that will tell you if you have water in it or use a Kolour Cote i think its called on a bit of hose and shove it down the filler to see if you have water. Missing and backfiring on a gas engine are caused bu a lot of ither things than dirty fuel in my experience

It's "Kolor Kut" water finding paste. A 3 oz. tube is 5 to 10 bucks. It's bronze colored and turns bright red when it contacts water. you just smear a little on a dip stick.

Also HEET is a good product to absorb water from gas. Walmart sells it, only buy the one in the red bottle. you can get a four pack for around 12 bucks. That will treat 60 gallons of fuel IIRC.

Thanks. Its been a while since i bunkered from drums so have not used it. Meths mixed into the tank used to make water go through the carbie just fine when i was a young bloke