Top-off tank

[kevinpaz]

I've built a little platform on wheels to hold a ~20 gallon tank so I can cart it around the house to all my different tanks (and stop running around with buckets).

My concern is if i use a glass/plexi tank all the back and forth movement (and water sloshing around) will weaken and possibly break the tank/seals. Can I safely use one of those big plastic rubbermaid containers? Will anything "seep" into the water if it's left there for days/week to condition the water?