Spuds, the uniseals are designed to fit curved surfaces... The pliable rubber expands to fill the hole when the pipe is pushed through it. They work on very small radius pipes as well as flat surfaces....thats is what they are for
Of course if you can get hte bucket to deform then a bulkhead would work... that certainly does not make what I said incorrect. Traditional bulkheads don't work well on curved surfaces.