Hi my bathtub drain is leaking but will only leak when tub is full of water ,and the plug pulled, then it leaks downstairs but... when tub is empty and plug is out and I let the water run into the tub and down the drain it does NOT leak why is that any help would be greatly appreciated

Thank you

You may have a very small hole or crack in your drain line under the tub and when you are just running water= the pressure in the tub there is not a great enough to leak or it is not enough water leaking to show up downstairs. When you fill the tub and then pull the plug that puts enough pressure on the leak or it leaks enough to show up. Do you have an access panel on the other side of the wall that is next to the drain end of the tub, if so you need to get into the opening and find out what is leaking. If you don't have the panel it might be wise for you to make one if it is feasible, because the damage will only get worse.

Thank you no I don't I have a tub surround but can access all drain fixtures in downstairs ceiling had to remove suspended ceiling tile in recroom now either me or my wife has to be downstairs with pail in hand to catch dripping water when tub is drained will get closer look

Thank you for responding