ISSUE:Grass Buildup On Gas Tank

I removed my gas tank on my YT 3000 this week for a good spring cleaning. I got the inside cleaned but cannot find anything that will dissolve the grass buildup of stains on the outside of this plastic tank.
I tried every household cleaner made, purchased some commercial cleaners, nothing seems to dissolve the grass stains. I currently have it submerged in a solution of pressure washer solvent, mixed with water.
This solution has removed all the grease and mold, but not these grass stains. I have looked on line and none of the solutions other people used will work. Several years ago, I purchased a solution that worked, which was a concreted pressure washer degreaser. I went to the local big box store and could not find it, but a dozen of so products that claim will work, bought several of them and tried them which was a waste
of time and money. I probably could use my pressure washer, but the problem is the tank is not bolted down and the pressure washer will blow it away. I cannot put it back in the mower to wash it,
can't get to the back side of it to wash it, plus I don't won't that crap all over my mower. It seems as if the grass and plastic tank have chemically bonded.

I would like to soak it a few days in a solution, if I could find a solution I know will work.

What have you used ?

post 917xxxxxx model number from under seat, you can purchase a new gas tank vs. trying different cleaners.

Nothing wrong with it, but the outside dirty.
Those puppies cost $73.45 plus tax & shipping. That's with no cap, which is an additional $25.40 plus new hoses. That was my first choice, except for the cost.
Still got the tank in the solution, slowly working.

I use "Super Clean" from O'Reilly Auto Parts, coupled with a 2000 PSI pressure washer. Don't know about gas tanks, but it cleans up stained mower wheels like new.

My only issue with it is that it attacks the seals in the spray bottle, and gets to the point where it won't spray any more. Eventually I just started putting it in a pump up chemical sprayer, which works great.

Nothing Works! I tried cleaning it with my smaller pressure washer and every chemical cleaner I had bought. I even tried scraping it with my knife, nothing comes off.
I did not try my larger pressure washer, 2800 psi, it would cut it into, but used the 1600 psi I have-which did not damage it.
It seems over a period of a couple of years, the grass had combined with the plastic, chemically and change its color from a light white to a light green.
So, I put it back on the mower and cutting grass. It don't look that good but the tank is hidden from view by the hood.

Maybe later on down the road I will replace it, but not for now. I should have washed it off, after each use.

Thanks for those who tried to help.

That is exactly right, the colour has bleed into the plastic.
If it really urks you the get some plastic paint & paint you tank
Otherwise a slight change of attitude.
It is a tool for doing work, not a garden ornament for looking at.