Even though there are other ways to flush an outboard that has been in salt water, these products are the only ones that completely immerse the entire propeller and gearbox system with fresh water. They are described as bags but they are rigid and self-supporting as you can see by the illustration. Suitabe for 30-60hp units. 

Features:

Completely collapsible for storage

Long lasting heavy duty material

Safe around petrol, solvents, etc.

Easy to clean out

Hose fitting connector

Dimensions: 600(Dia.) x 600(H)mm