dyntopo: Effectively remove redundant polygons

When sculpting with dyntopo enabled it’s easy to make the poly count go op drastically. Some of my areas have too many triangles, even though the area does not need that level of detail.

What I do so far is go for the clay brush and lower the detail, collapse edge enabled, and then brush away.
But sometimes I also scrape too much away from the surrounding polygons. Is there a more effective way of doing this? I wouldn’t mind if I have to switch to edit mode. As long it’s quick and efficient.

I was already using your first method but it works rather inaccurate with the zooming mechanic.
I’m already using v2.71 and worked with the new feature, just never considered floodfill would also work on masked areas. Ill try that. Thanks!