After some tedious preperation, you should be able to rid the unwanted taste and smell! But I have to admit, it was the best work to do, it's quite a disgusting labour.
This is what I've done with it:
1. give it a good rinse in the sink to rid the seaweed and other particles on the shell
2. using a pair of good cooking scissors, make an incision on the soft tissue surrounding the beak. Cut a circle around 1" to 1.5" from the beak.
3. lightly rinse the innards with a slow and steady stream of tap water
4. look into the shell, and cut along the wall with minimal flesh attached. (like splitting an orange)
5. carefully seperate the flesh with the sewage colored/smelling membrane and scope out the flesh with a small spoon.
6. rinse flesh under a slow and steady stream of tap water
7. soak a little in a big bowl of salted cold water
8. take out, and pat dry with kitchen towel
9. place on plate and cover with saran wrap and place in fridge for at least 30 - 60mins before serving.
It does take time, but you'll be rewarded with the most delicate uni flesh when done right! Good luck and good eat!
mine is different,
use kitchen knife cut it into half
scope out the flesh and put it in you palm
rinse flesh under a slow and steady stream of tap water
take out, and pat dry with kitchen towel