You can almost certainly ignore what is actually chemically safe or sensible.
The thing you should comply with are your local laws which will be much, much stricter than is actually required - the reason for compliance being that you can probably get a large fine by not following the regulations, however excessive they may be. Some part of your local government will have a PDF file, or a human, that will answer your questions.
Bearing in mind that the largest component of your leftover chemistry will be water, one approach is to let it evaporate. This reduces the volume and weight of your problem considerably.