Remove the rad cap, pull all the plugs, insert the compression tester hose ( sans valve ) into a cylinder. Rotate the engine by hand ( either by crank pulley or a socket on the alternator pulley ) , listen / feel for air coming out of the hose _while you are turning_. When the air stops the piston will be very close to TDC / both valves closed.

Roll the motor back and forth, feel for a point where there is little resistance to turning, center this point. This low resistance is due to crank turning but pistons not moving.

Mark the crank pulley if you like, be sure to remove any tools from the crank / alternator. Hold the quick connect sleeve on the air hose back, do a quick plug / unplug so a puff of air enters the cylinder. If the engine does not turn, rehook the air then look for bubbles in the rad cap. Leave it attached for a minute or so.

If the motor rolls over, turn and try again. The trick is a short puff of air so the motor does not roll over too far so you can find TDC rapidly.

You _will_ get air leaking out of other areas, don't be alarmed. There will be hissing in the oil cap ( rings ) out the tail pipe ( exhaust valves ) , sometimes air filter ( intake valves ) and if the head gasket failed between cylinders, the next spark plug hole ( OK, now you can be alarmed, these are listed in order of engine wear.) .

The exhaust sensing fluid that you put over the rad cap won't find small leaks, a leakdown with air is the only way to test engine health.