@Skip Yes just mute the instance (option under the three dots)
@Skip
An easier way -- if you see a post coming from one of those adult domains in the Federated feed, open the post and you should be able to do it from there.
1. Click on the post to expand it.
2. click on the username at the top. It will open their profile page.
3. select the dots menu, and Hide everything from ... the instance.