Some of the buckets are mounted high, others low on the boosters. The high ones wouldn't be too good at catching fluids. That's why I'm intrigued. For fluids that come out during transition to vertical, you'd think they would just have cans sitting on the ground to attach the hoses to.

I've always assumed they transported the boosters empty. They don't need pressurization to stay together so it shouldn't be any residuals from the main tanks. If you've seen the depleted boosters after they crash land back on earth, they are still in remarkably good condition.

Could there be a subsystem that has something that boils off and needs a catch can like some folks do with vapors coming out of engine valve covers? The hoses terminate into a blanket covered area of the booster.

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