I have a 1950's toilet that leaks into the bowl through the flapper. It differs from modern toilets (this question) in that the outlet pipe is made of brass. I am not inclined to replace the toilet because it is pink in an entirely pink bathroom. (I am inclined to replace the whole bathroom, but not yet.) I have replaced the flapper rubber.
We noticed that the brass out pipe is not completely flat, and has undulations that cannot be smoothed out with sandpaper because they are too wide. I figure that the whole pipe end needs to be brought back to true, but the only thing I could think of was to use a detail sander on it for a few minutes. This seems to have mostly got rid of the undulations, but I cannot be certain (suggestions?). The flow has now reduced from about 1 litre/minute to less than 0.2 litres/min, but this will still cost me about $45/quarter in water charges so I would like to go further. Is there a better way to bring the pipe back to a true flat surface? How can I determine when it is flat?