Wife left the bath gray tank cracked just a little. Was solid ice the whole dump pipe, got what I can see thawed with a blow dryer and currently have a blow dryer into the pipe.

It's only 25deg out and when I go to dump gray tank nothing still comes out. With blow dryer into the outlet pipe water is still dripping out.

How deep can this ice melt go with tank heaters on? Ay other suggestions what to do?