I'm looking to use por15 tank seal in my twin tanks is there filters inside the tanks that might need removing first

Yes. There is a nylon strainer in there. They are mounted directly on the ends of the pick-up pipes, fairly difficult to see (I put an inspection camera in there, that was how I found them). The one on the LH tank you could probably get off through the sender hole. The RH tank, well, have fun!

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