From my days working on arranging the de-commissioning of underground fuel tanks for Esso filling stations, IIRC the best way to de-gas a fuel tank is by using nitro-foam. It works sort of in the same way as hot water and fairy liquid; apart from disposing of the waste material. The 'bubbles' force all the explosive gases out then eventually dissolves and evaporates. Cheaper and quicker than to fill with water and obviously not a problem with disposal.
Part 27. On all the carbed SS models with half fairing unless the higher level oil cooler is fitted. IIRC doesn't apply to the 600 because the cooler is up underneath the headlight. But actually it isn't really needed if the other fixings are all good.