You can fill in the fields to create a feed you like, save it and it can be found under the drop down menu, forums, my active feeds. That will then stay there.
if you want to make that the go to search when you hit the new posts tab next time you click on it and it loads. next to the title a the top theres a greyed out tick it, Press that it turns green and it makes it the active search on the new posts button (rolled up newspaper)
I've done this so i get every post from the last 2 weeks, read, commented, etc etc