bulk head fittings

After looking up I see some people having it on both sides.

Yeah i would agree. You might be able to get away with them on just the inside. Might as well get progressive for that shit.

I always put mine on both sides. Mine ended up becoming brittle and cracking. I'm not going to blame it on E85, but it was the E85.

I can't imagine you need it on both sides, it just means you lose tightening torque with more compressible material, possibly leading to overtightening… maybe with extra large washers to spread the load more I'd consider it

That said, I don't believe you need it on both sides to seal effectively, placing it on the cleaner inside makes more sense, but I have to ask, why not copper crush washer at that point?

Nylon crushes too and will be fine for what I'm doing.

Get rid of bulk heads, weld bungs. After they get brittle and fall apart you will try to figure out where that fuel smell is coming from.

Can always go copper crush washer when that happens, but considering everyone uses nylon I don't think it will be an issue. I break down this car every year or so I'm not too worried. Still have to build in my custom studs for the electrical.

For sealed electrical connections I'm going to get a m8 nylon screw and tap it for m6 or m5 stud. Then use a nylon lock nut with some sealant to seal together. Anyone have a better solution that won't be electrical plugs from summit that are 1 1/4" thick.

Good idea I have been thinking about doing that for years now.

This is exactly how I have mine set up.
I have the nylon washer on both sides.