Very old Standard toilet in my shop building. Water in the tank is as high as it can be adjusted to. If you flush and hold the handle it doesn't empty the bowl. If you flush and dump a container of water in the bowl when you flush it will empty completely. Septic line is clear and the sink works as it should. Have used a commode snake on the toilet and it's all clear. I'm thinking it's time for a new toilet but would like to understand what's going on.