It simply means that they dictate how this should be disposed off and you have to adhere with their guidelines. Contact your local authority, many years ago, I found some chemical drums in a basement and didnt know what to do with them but definitely wanted shot of them. I called the local councils waste team and they picked them up for me.

Is this the same PCP that had (has?) a certain reputation in the wacky backy stakes? Worth a call to the original suppliers if they are still around and if it's an algicide, it's not one for the drain without checking in detail first. There are some common phrases in MSDS as drafted by US lawyers about disposal per local ordinances and it sounds like you have one of them. Vapid and useless - no, I mean the wording not the author. Or both perhaps...? Worth a hunt for an up to date European version.