Sometimes, though, there's no reasonable alternative. I've been struggling with the first three chapters of INSURGENTS (working title). At first I thought it was just the pain of starting to write again after several weeks off; when I start a new book I always mope around the house for the first few days complaining that I've forgotten how hard it is to write. So I didn't immediately recognize the Second Law of Writing, which is that if you are agonizing and struggling to write a scene there is probably something wrong with it. After all, these opening chapters did everything I wanted them to: show a rebel raid on an outpost, bring my two main characters together, set up that they're going to have to stay together for some time whether they like it or not, and create a new problem for the rebels arising from the raid.
The only problem was that it wasn't believable. The outpost was seriously undermanned for no reason, my secondary character had no good reason for being there, the ruse that made the raid possible wouldn't work, even if it did the raid would only succeed if the invaders did a whole slew of stupid things... Well, I fixed this and explained that; asked my First Reader to take a look at it; he pointed out some new problems; while he was reading I noticed some other problems.
Then I realized that I was putting patches on top of patches to save a structure that was unsound in the beginning.
That's when you're "washing garbage." When, no matter how much you change words and dialog and insert explanatory background, you're still working with a fundamentally flawed idea. And it's still going to smell like dead fish and coffee grounds no matter how often you wash it.
So, this weekend, eleven thousand words went into the recycling bin and I spent most of my time reading books on guerrilla warfare and IED's in the hope of shaking a new idea loose. (If anyone's interested, the book I found most useful was The Other Side of the Mountain: Mujahideen Tactics in the Soviet-Afghan War and the least useful was Mao's Guerrilla Warfare.
Now, I hope, I've got an entirely new surface plot with the same deep plot (those things I wanted to accomplish in the opening chapters) underlying it.
Let's see how hard it is to write this version.