Best way to trim rim

[aellis9369]

What's the best way to trim about a centimeter chunk out the rim? I can't afford to drill out a fourth tank, and this rim goes lower than the last one, blocking my overflow from fitting
Edit just for clarity: i dont want to remove the rim, just cut the bare minimum for clearance

 

[KrisReef]

It would be messy, but if I had to do this I would use a grinder. I might not look very good when it was finished, either.

 

[19Mateo83]

A hot butter knife will melt through the plastic easily.

 

[Keywest99]

Do you need to trim just a small section? If so, I used an exacto knife/razor blade to fit two 3/4 inch 90 degree fittings in mine. No mess.

 

[ryanjohn1]

I would opt for a dremel

 

[aellis9369]

Thanks yall. The suggestion of blowtorching a knife (is it bad I don't have a normal lighter) worked on scrap plastic in the garage. It did throw some fumes out, so I'm just waiting until my newborn isn't home to commit