Technical What to use to clean out a poly gas tank with? Environmental police need not reply;)

So a few years back I added gas to a tank. As I always do, I never pour it out for the last drop…I take the last bit and it becomes instant weed killer.
When I did that, I noticed the fuel in the can I used (can hadn’t been used in years, just inside the shop) rusty gas came out. Didn’t worry about it then, figured the sock and filter would take care of it. Started the car and ran it around for a bit and pulled it into its resting place where it’s been for 3/4 years.
In a few weeks I’m going to pull the tank, kill some more weeds, and use the tank in my kids car.
I know most of the rusty flakes will pour out, but I’m sure there will be some residue of nasty stuff in there.
Ideas?

 

Poly ? Plastic ? Why are there rusty flakes in it ?

 

I a bit confused. Is the tank poly or steel? If poly you might just use some Simple Green. If steel, my go to rust remover is white vinegar. Let it sit a day or two depending on how dirty. After getting it clean, rinse with baking soda and water. The used vinegar is a good yard ant killer.

 

Maybe I didn’t explain it well? When I poured out the gas from the metal 5 gallon tank, rusty gas came out of the can, I could see the flakes. Yes, should have looked inside it before, but heck, was fine 10 years earlier
So poly/plastic, whoever OEM mid 90’s GM vehicles use is the tank I want to clean.

I can put a spot light on the tank and seen the dark discoloration in the bottom. 2 inches or so.

I raised the rear of the car from the differential with my floor jack, to see if it was just the fuel left in there making it look darker. The “darkness” level didn’t change.

 

Not sure if that could work, the tank has a baffle in it. Also would be difficult through the filler neck.
I was thinking of some type of something to pour in and slosh around.

 

That’s worth a shot.
Thanks!

 

Purple Power comes in jugs and it cleans well, doesn't leave a "film" when it dries

 

All the late model poly tanks that I have cleaned don't have a baffle. I take the tank off and wash with a pressure washer through the filler neck and sending unit hole. Drain it and let it dry out.

 

Citric Acid mixed with water will remove the rust and also clean the plastic and is mild enough to not hurt anything. Pretty cheap to mix enough for a gas tank and safe to dispose of.

 

The filler hole on the Harwood fuel cell in my Austin unbolts and makes cleaning it a snap. Trying to clean out rust flakes without removing the filler will be difficult to get it all since you have a lip that hangs down into the cell and it wont let all the debris flow out.
The inside flange is two pieces, so it can fit through a smaller opening. and there are nuts inside also that need to be held as you tighten or loosen the top. But it's pretty easy to R&R the filler, and then washing it out with just any decent cleaner will get everything out of it.

 

Install a nylon 1/8-27 NPT drain plug in the bottom of the poly tank and use it to drain the tank of the cleaner you plan to use like mineral spirits. I did this 9 years ago and it still works fine. Here's the thread I posted about this on Fordbarn years ago. I have removed and re- installed the same plug many times since and it still does not leak.
Installed Drain Plug in Plastic Gas Tank - The Ford Barn
I use this thread sealer as an extra precaution. Most auto supply stores have it.
Amazon.com: Seal-All 380112 Contact Adhesive and Sealant - 2 fl oz, Steel : Industrial & Scientific

 

Could be worse, I'm cleaning out the tank on my 29 Buick. I don't know what it is, almost a dried out rusted foam? The steel isn't too bad if you ignore the holes.

 

Those chunks are the disintegrated baffles inside the tank.
Your fuel filters will continuously clog up if you keep using that tank.
Hate to say it but, it's time for a new tank for your 29 Buick.

 

If time is not much of a factor, I would pour some type of mild acid solution in it and buy one of those packs of BBs at Tractor Supply and pour them in the tank. Then put it in the back of your pickup truck and drive around for a few weeks.
I cleaned the inside of a very small tank by clamping it in my paint shaker with BBs inside and some Por 15 cleaner.

https://www.tractorsupply.com/tsc/product/daisy-6000-count-bb-bottle

 

30 years ago I cleaned a steel tank by strapping it to a cement mixer, a couple gallons of gravel, and about 5 gallons of water, blocked all the passages, turn it on and let it rip. I think it was about 3 days. Emptied it out, flushed it several times.....worked perfectly!! That was steel, I don't know about poly.

 

Water and Dawn detergent?

 

As I mentioned before, I have cleaned out numerous late model poly tanks with just a pressure washer. It is amazing how many put diesel fuel in gas pickup trucks and vice versa. They usually have huge holes for the sending units where you can stick your whole arm in with a sponge to get all the water out. On ones for vintage Fords, not so much.

 

Take it to the carwash and blast it out with hot soapy water, remember to use a face shield.

 

https://www.zoro.com/crc-5-gal-brak...0fffd17e13c818fb9514b58036a30b2e&gclsrc=3p.ds