Printing material for methanol tank I am trying to print a tank to be used with my RC engine. The material that I have to use needs to have the following properties:

It needs to be possible to seal the final print so that it is not leaking any fluid
It needs to resist methanol, nitromethane (a solvent like Acetone) and lubricating oil at room temperature. It can get discolored or have other changes from the fuel, but it must not be able to compromise the sealing.

I first - foolishly - just printed it with ABS as I do for every fluid container as I can nicely seal it with Acetone. After almost being done with it a friend told me to check the chemical resistance of ABS and as you might guess methanol and nitromethane completely desintegrate it, almost like acetone itself, so that was a waste of time/material.
Next I considered using Nylon. It shows exactly the chemical resistance against all the fuel components I need, however I could not find any (easily available) option to seal the print after printing and after printing a small test container and pouring in some water it leaks after half a minute, so unless I find a way to seal the Nylon containers interior this is also not an option.
I checked various epoxies but the few that I checked all showed poor resistance against methanol/nitromethane.
What I could not test yet but seems like an option is using HDPE. I am using PET bottles to transport the fuel sometimes so it definitely is both resistant and - in theory - watertight, however I am not sure how I can seal an HDPE print, so I am not sure about my first requirement with HDPE. EDIT: I found that Limonene dissolves HDPE and is relatively harmless and easily obtainable. Maybe it can be used to seal the HDPE print surface?
Hence my question: Is there a material that can be printed on a regular desktop printer (heated bed, nozzle up to 255°C) that satisfies both my requirements above or am I &quot;doomed&quot; to buy a moulded plastic fuel tank?
Most commercial blow-molded fuel tanks for model airplane fuel (methanol or ethanol, nitromethane or nitroethane, and some combination of castor, mineral, or synthetic lubricating oil) are made from HDPE.  This material isn't commonly seen as filament, in my limited experience, but it ought to be possible to arrive at settings that will give a liquid tight tank without further sealing if you can find some.  As you note, limonene might be used to smooth/seal HDPE prints, but likely won't be necessary if your settings are right.
You might want to test PETG filament for its resistance to your fuel mix(es) -- this material is available as filament, prints with settings little different from generic PLA (in my experience, higher nozzle and bed temperature, and a little more bed clearance for the first layer), with good layer adhesion and, with a good print, is liquid-tight as printed.  It's not particularly flexible (as is the case with HDPE), but since you can customize the shape of your fuel tank, it may work for you -- or it may be more flexible in vase mode, as PLA is.
Sealing PETG may be as simple as baking it (similar to &quot;heat treating&quot; PLA to increase print strength, albeit again at a higher temperature) -- this partial remelting will ensure that layers are adhered throughout the print, which (presuming you have avoided under-extruded areas) should be all that's needed to make a printed tank liquid tight.