125, I have a 530 with the original single filter body under the tank, that gave me trouble so I went to the hardware store and picked up a 3/8 th inch 1/4 turn brass ball valve and hardware to screw into where the present drain goes and hardware to get down to the line size at the filter line, Lots more volume since 3/8 comes out of the bottom, if you wanted to have a drain you could use a Tee out of the tank and put a valve on the bottom. I will try to add a pic in another note.
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