Hi Mike,
If I were you I would buy new sand for the 150... stiring up the sand in the 72 could be fatal for your corals and it will take more than a litte water to clean a years worth of crap from the sandbed.... I removed my 1 year old sand bed a while ago when I had the tank broken down, and made the mistake of leaving the 2" sandbed in 2" of stagnant water overnight... lets just say my room mate was less than impressed with the odour permiating the entire house for the price of new sand vs the price of new livestock I say replace it and start again with that sweet virgin sand look
or go BB like I did
Dan