The problem of increasing numbers of small pleasurecraft and resulting increases in the pollution problems resulting from the sanitary wastes from these crafts has caused much concern. Formerly the waste from these crafts was dumped into the surrounding water, causing major pollution difficulties. Of the several possible means of handling sanitary waste from small pleasurecrafts, the most direct would be storing of the waste until it could be disposed of on shore, perhaps after treatment. One of the main problems in development of such a disposal system in small crafts is the probable lack of space for installation of a holding tank. A means of overcoming this obstacle has been sought through the use of a flexible holding tank which could allow for installation in hidden and almost inaccessible places with a minimum of structural changes. The design criteria calls for an accordion-pleated tank to be made of elastomer coated nylon fabric with ten 60 degree v-shaped pleats with a cross section of 14 inch by 24 inch and holding about 18 gallons of fluid. This tank could collapse to fit a much more restrictive space and can actually expand to 21 inches to provide a capacity of nearly 25 gallons. The results showed that a tank of the specified materials provides an acceptable and versatile holding tank for upgrading a sanitary system on small pleasurecraft, particularly in the 22 to 28 foot length.