We*had a 40' GB that had the tanks replaced years ago and was in need of cleaning. The PO had the old tanks replaced with two aluminum tanks, stacked, both port and stb'd. This application made it impossible (due to cost) to clean the upper tanks so we opted to clean only the lower two tanks. This required cutting, drilling, tapping hole, fabricationing plates & gaskets. Tanks were approximately four feet long so two holes were cut in to each tank, one forward, on aft*so our cleaning process could take place. Getting to the tanks in this vessle was pretty straight forward, most of the time we have to have a shipwright come in*to make access for us to get to the top of the tanks.