TMI Warning
We have a round toilet bowl in our apartment (building constructed around 1960).
An older man has difficulty cleaning himself because water level is high.
How would one lower the water level to cover just the draining point. See pictures below for water level and toilet structure.
Usually water level is determined by the height of the siphon bottom. Any liquid higher than that will drain to sewer line. That's not adjustable on a toilet, as it's in the shape of the porcelain tubing cast into the stool. You should be able to kludge things to a lower lever by adding a piece of flexible tubing which goes drops further into the bowl, and the waste line than does the original porcelain. However, that's going to be problematic, as it'll be prone to clogging and make the toilet harder to clean. Only real option is to replace the toilet with one that behaves as you want. Some extra tall toilets give more room between the seat and the water level.
The shape of the outflow channel determines the maximum amount of water that can rest in the bowl, but the momentum of the water in a flush would leave the level lower than the maximum. Therefore, water is trickled in after the main flush to bring the level up to or near the maximum. In a standard gravity toilet this trickle is via a small tube going into the overflow tube, but this is not adjustable AFIK. I wonder if it is adjustable in this commercial flush valve?
But IMHO the level in this toilet is fine. If a particular user thinks they could benefit from a lower level, they could lower the level before use with a couple of downward strokes with a plumber's plunger.
Your bowl has a gallon rating. Use a diaphragm that's smaller or a smaller relief valve to reduce the amount of water.
Reduce the amount of water that enters the bowl after a flush
The bowl gets refilled by the tank after a flush. If you change the tube so less water goes into the bowl, then the water level will be lower.
You can also use an adjustable clamp and use that to adjust how much water goes into the bowl.
If that still doesn't work, you can drill holes into the tube so that some water leaks into the tank before going into the bowl. Obviously this is non-reversible, so do this only as a last resort.
You can also completely remove the tube so that the absolute minimum of water is in the bowl, but that may risk having sewer gas come through if the water level leaves air gaps in the toilet.
