I’m starting to wonder what I got into here… Just picked up a 1990 K75S, my first K-bike. I can’t keep gas in it: fuel comes out the drain line at my right foot.

As part of the ‘new-to-me’ service, I replaced the fuel filter. While in there I checked the hoses and everything looks as it should, nothing loose or suspicious. The tank does not have a ‘burrito’, but the top couple cm of the tank appears to be a chamber of some sort that is probably serving the same purpose as the burrito. I just got back from an 85-mile shakedown ride: I started with a full tank and ended with the fuel warning light coming on just as I got home. I checked, and the fuel warning light is correct: there’s ‘slosh’ left in the tank and that’s about it.

Other possibly-useful information:
1) no, it’s not running rich. The plugs (changed them as part of the new-to-me service) look good, certainly not 17mpg rich. The gas is exiting at my right heel, not the tailpipe.
2) Yeah, it’s liquid gas, ml at a time, not vapor.
3) The tank has been sealed. There’s some sort of coating all over the inside, streaky in places. I’ve attached a photo taken inside the tank.

So… what’s up? I believe that the return overpressure line from the fuel rail comes back to the collection chamber, and the vent comes from the collection chamber: could the coating application have blocked drain holes to that chamber so that the fuel rail return is just pumping gas out the vent line? What else might be going on? Would it damage anything if I disconnected the fuel rail return hose inside the tank? What else could be causing this? Any suggestions?

Hoping someone can help me confirm my diagnosis or point out anything I might be missing.
— Fuel pump is audible on ignition on

Please clarify.

Does this statement indicate that when the ignition switch is turned to ON, the fuel pump can be heard running before the starter button is pressed? If so, that should not be happening with a K75 LE Jetronic engine control system, and has little to do with the Hall sensors themselves .

Put her on the side stand and see what you see. It should show low or nothing if sight glass is just covered due to high oil level.
 Otherwise, yes, sight glass replacement happens from outside. It's just a plastic disc with seal.
 The "reflector" behind it is somewhat important,  though....

I just saw Snowbum's procedure with a heated screw driver so 2) is answered! https://bmwmotorcycletech.info/sightglass.htm

Looks like it passed the static test.
Did you do the dynamic hall sensor test from the first reply?