Thank you to everyone who answered. Using the 'trace the fuel line method', I was able to find the filter (I never would have guessed it would come out of the TOP of the tank instead of the side or bottom )
. Drained some fluid from it, but it was next to impossible to see any differentiation in color from my position under the bus, so I had to guess when to stop. How much water is necessary to make the water light go off? How much fluid is "too much" and puts me in danger of losing the pump prime?