Almost all the toilets I work on are supplied with 3/8 in lines fed by a 3/8 compression outlet supply valve EXCEPT the LoBoy toilets which all seem to use 1/2 in compression outlet valves and 1/2 in lines. Why this pattern?

My best guess - since bowl wash occurs during fill, a higher volume of water flow is required during fill.



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i believe some of the water from the fill valve is forced down a passage to help create a swirling action.

Just an installer's preference. I have never done it that way and the toilets ALL flush perfectly. In any case, regardless of the connection sizes on the ends of the supply lines, the hoses themselves are equal.



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The LoBoy toilets I encounter are old ones, installed at least 25 years ago and the lines are 1/2 in copper tubing, not flexible hoses.

Maybe it is a Toronto thing but all the LoBoy toilets I come across have the 1/2 supply lines and, if it is not a LoBoy then have the 3/8 in lines. This must have been a standard practice among Toronto plumbers from decades ago.

The 1B1X replacement fill valves for the LoBoy toilets have large internal passages for high flow. It looks to me like 1/2 in was used to accomodate the high flow fill valves in LoBoy toilets. My hypothesis, anyway.