TOPIC:

I'm planning to remove the superficial rust in my tank using the Klean Strip iron phosphate cleaner, as has been recommended here.

My question is, should I remove the fuel level sensor before using this cleaner? If I leave it in place will it be damaged, or just cleaned up with the rest of the tank? Mostly I ask because it will be more of a hassle to slosh around the cleaner without the sensor in place.

I'd suggest the fuel level float assembly be removed. Make a cover plate to replace it,

I used a solid conical rubber plug in place of the fuel cap in case it leaked onto the tank paint with success.
The plugs were sourced from the marine shop some years ago.
Also removed the fuel petcock because it had a leak and made a sealing plate to block that opening.
I used a small round 50mm plastic measuring cup for the fuel sensor opening ( surprising how strong they are !) and with those two plugs in place poured in the recommended dilution rate of "rust wash (50% phosphoric acid)" , shook it around and let stand for a while followed by more shaking and standing. Repeated the operation a couple of times and the tank turned out great . I also played around with the dilution rate to speed up the reaction time