Based on your info, it would appeared that your fuse tap is not working.
The red arrow in the pic below pointing to the Active tooth of the fuse tap. That need to match up with the live point in your fuse
.
Here is another test to verify that your fuse tap is working.
1 - Remove the 15A wiper fuse again.
2 - Plug the wiper fused that you removed into the bottom slot nearest teeth as shown in pic
3 - Leave the other fuse slot empty.
4 - Plug fuse tap back into wiper fuse box
5 - Start car and test wiper.
If wiper work, then you know that your fusetap is good. if wiper do not then that fuse tap is cactus - get a new fuse tap