I have mentioned this before but for myself I made a device to soak rolled tatami omote which can be stood up in the corner of the bathroom shower or garage corner or stored almost anywhere conviently. It consists of a PVC pipe and a stopper at each end. simply roll up the tatami tightly and tie off. I use rubber bands for convience myself, drop the prepared roll down the tube, add water, and then plug the open end with the stopper. The stoppers can be purchased at Home Depot for about $5.50. One PVC pipe cut in half and four stoppers works fine or you can use two PVC caps and glue to seal the end of each pipe and will only need two stoppers. Frankly the caps and glue cost almost as much as the stopper. Another plus is that you do not have a large tub of water sitting around to freeze or harbor mosquitoes.

I have a video showing the soaker tube and how it is used.

http://www.youtube.com/watch?v=17czx2hHSiw

Humm video is unavailable...

Humm interesting idea. The only downside is needing a bunch of them since if I'm gonna cut tatami and have to wait a day for it to soak, I'm gonna do it in large batches ;) .

we use pickle barrels or the large rubbermaid containers which can soak about 15-20 at a time... need to use a few bricks or buckets to hold the mats down... the pickle barrel has a lid.