I just moved my 150 which had a DSB that was up for 3 years...I'll be rinsing the sand, but the point I want to make is this:
This bed was built on a plenum. Now I know there are studies showing this doesn't result in more effecient denitrifaction, however I have read that it keeps toxic areas from forming by allowing a small amount of movement under the bed.
I have moved my tank several times in the last 5 years and before this last move I never used a plenum and the sand was STINKY!! when taking it out...not so with the plenum...don't know if means anything but I'll always use one now.
I'm a firm believer in DSBs and have used them every since I got into the hobby 15 years ago.