Korky makes the fill valves,
Here are instructions below
Hi, We have had 2 Toto toilets for about 6 years -- Carusoe Gravity and Ultimate Power Gravity. We have had no trouble at all with the Carusoe, but we have had to replace the fill valve 2 times on the Ultimate Power Gravity and it is now time to replace it again. About half way through the fill cycle it starts to whistle and hiss-hiss-hiss; psst-ppsst-ppsstt; all while spraying a jet of water out the slots in the top of the valve. While doing a search for a replacement TSUO4A.5 Toto Power Gravity Fill Value, I stumbled across some information that seemed to indicate I could replace the Power Gravity valve with the G-Max fill valve because they are the same size (3"). Is this really a viable option? Is the G-Max valve be a longer lasting valve than the Power Gravity one? If this is something you would recommend, will you please provide information to find a replacement G-Max fill valve (like the part no.)? Thanks!