I have several smallish decks around the house that were treated with crap Thompson's Water Seal about 5 years ago (not sure exactly which variety).  On those decks that get tons of Southern California sun and heat, the Thompson's is pretty much gone.  In shaded areas (or under furniture) it's still there in varying states of decay.

On my smallest deck, I've been trying to prep the deck for a new stain (that I chose based on your recommendations - thanks!).  It had a combination of space with and without the old sealer.  First I tried Restore-a-Deck cleaner.  Did a nice job cleaning, but didn't remove the Thompson's.  Then I tried Restore-a-Deck stripper.  While I didn't pressure wash, I did a lot of hand scrubbing.  Some of the Thompson's came off, but most of it didn't.

What do I try next?  Will the pressure washer be more effective at removing the Thompson's?  Do I need to just give up and sand it all down?  In which case, I probably have to sand the whole deck to get a consistent look, right?  I'd have to rent a pressure washer or good sander... Do I just need to hire somebody who's got the tools and experience and more muscle than I do?  Ack!