Are the fuel filter connections supposed to have washers/any kind of seal?

Just replaced the fuel filter on my 03 V6 at 250k miles with an OEM toyota denso one. Didn't see any washers/seals on the inside of the old filter or on the compression nuts and didn't see any on the toyota EPC. Don't know if it was the original filter as I'm not the original owner but it was also an OEM toyota denso one.

When I tightened both compression nuts on the new filter to a level that I thought was tight enough and thought I'd done the job properly, I started the engine and it began squirting out gas from both sides of the filter. I crawled back underneath and tightened it more, and the leaks slowed down quite a bit but not fully, then I got underneath once again and tightened it more (until the point where I felt if I went any tighter, the bolts would round off or something would break) and finally the leaks stopped and everything was nice and dry.

Just curious if it's normal to have to use such a high amount of torque on these fuel filter connections to get them to seal properly or if there's some kind of seal that is supposed to be used.

I used the correct part number filter (same as the one I took off), nothing was cross threaded (I was able to screw the nuts in by hand before torquing them down) and the threads on the fuel line bolts all looked to be in good shape. The inner holes of the new filter looked perfectly round and machined correctly.

Glad I did the job, the old one was dripping out black gas from one side and clean gas from the other. But was just curious about this.

 

With compression fittings, the flared pipe ends themselves are the gasket. I haven't done this job before, but in general, they need enough torque to make the pipe metal conform perfectly and form a gasket.

 

That makes sense. Thank you.