One solution is to raise up the "platform" and collect the greywater in 5 gallon buckets that ARE the very structure that is elevating the shower platform. Caretaker of shower system can then reduce time maintaining system as it will handle about 14 gallons before need to transfer greywater to containers or evaporators.
Although I've posted some of the "how to do it" instructional pictures before, I've added more:
http://goo.gl/1qusQ