If the client is using TinyMCE to edit the content field, the richtext content is what's stored in the DB for that field. Your only options are:
1. Write CSS that handles the richtext content (TinyMCE's output is standard HTML).
2. Use the stripTags output modifier and have no formatting at all (i.e. raw text).
3. Convince the client to give up TinyMCE.
If you can teach the client not to use the enter key except at the end of a paragraph and leave a blank line between paragraphs, #3 might work for you.
I've actually had some luck getting clients to write in raw HTML using only a handful of tags. You can also try getting the client to use an HTML (non-rich-text) editor that will check the code for them and have them paste the results into the content field. I think the FF add-on "It's All Text" will do that also -- it would let them edit the content in place in the Manager (sort of).
You might also be able to customize TinyMCE to restrict them to a small number of possible tags.
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