I installed a new complete Fluidmaster and filled it up with water but when flushing water comes out under the tank not under the toilet though.

If you have a low profile toilet, usually 1.6 gallon capacity, then the toilet rim wash originally came with a more complicated fill valve that diverts the initial flush of water into the rim through a plastic tube inserted in a rim wash hole in the center front of the tank, (this happens a second before the rest of the water flows into the bowl,to insure that the rim gets cleaned properly while there is still a greater supply of water in that little tank for gravity to do the job.) The rest of the water gets into the tank from where the flapper raises up. My idea to fix my low profile toilet using the fluidmaster, was that instead of hooking the tube from the fluidmaster onto the overflow port, I just used a longer piece of tubing that would reach into the rim wash hole. The hole originally had a 1/2" by about 6" white plastic tube stuck in it, and then the original rim wash tube fit into that. For my use, I just removed the white plastic tube and put the other end of the 1/4" tubing from the fluidmaster directly into the rim wash hole as far as it would go.

What I have learned with my DIY toilet repair, is that in a regular size commode the rim wash is fed through the overflow tube, but in a low profile the rim wash is ONLY fed through that center hole and tube. And you don't need a tube in the overflow, because the rim wash works as the overflow.

I also learned that although the tank measures 9" from tank floor to top, and much of the packaging on the universal fill valves gives a measurement of from 9 to 13 or 14 inches. However, what really matters is not whether the unit will fit inside the tank and the lid still close, but where the top of the overflow port is in relation to the mechanism on the fill valve, so the new fill valve will shut off completely. I tried the Korky brand on mine and lowered it as far as it would go, and it was just 1/32" too high and that's all it takes for the thing to keep trying to refill the toilet. (If you can't hear well, but you see bubbles around the flapper or near and at the bottom of the valve long after the flush has completed, then you have a leak somewhere, likely the flapper if it is a leak, or the fill valve is not shutting off because it can't be adjusted down low enough in relation to the overflow port. The fluidmaster is not as pretty but it does work for my toilet. A couple of times a year I have to reach in and adjust the sliding float wire, and that is certainly better than the real toilet replacement parts at over $200.00. For a few pieces of white plastic? No way!

Probably needs a "doughnut" tank washer under tank..or try tightening the tank bolt..fluid master comes with a little rubber hose that goes to overflow tube