Adding Spigot to Roughneck

[Maverick00]

I plan on getting a 20G rubbermaid roughneck to use as 15gal water change vessel.The rubbermaid will be lifted higher than the sump with a spigot at the bottom to gravity feed into the sump after the saltwater has been mixed and brought up to temp. What kind of connection would you guys use for the spigot? At first i was thinking of just a pvc bulkhead fitting but im not sure how it would seal with the curvature of the rubbermaid. Anyone done something like this or have any ideas?