Are there any toilets that dump on the track now? I'm almost sure that the 321s do but perhaps they have had tanks fitted. Has Northern and EMR locked out the toilets on the 153s?
I'm fairly certain that any train that's had one of the standard modular universal toilets fitted will now also have waste tanks, as they tend to be installed together despite the two issues being dealt with by different rules. Older accessible toilets (such as on 158s) would have still dumped on the track but I believe all are tanked now.
Dumping on the tracks was supposed to end at the turn of last year but surprisingly wasn't as much of a political issue as accessibility was, until Covid came along and focused attention on things like hygiene. A number of media outlets have run stories on how some of Britain's trains were still doing this during 2020.
I wasn't aware of a specific new deadline for this new year, but whether it's a law or a policy change it's as good a time as any to make a change- and a very welcome change too for those who work on our tracks or clean and maintain our trains.
It's a good thing we're in Lockdown 33⅓ in a way, as otherwise these decommissioned toilets would need bolting or welding shut to stop people breaking into them on the late night "Vomit Comets"!
No idea if Northern or EMR have done similar but I wouldn't be surprised. The only non-tanked loos on trains still in traffic I can think of are the 143s and the 153s you mention, I'm assuming all EMR's HST trailers now have tanks fitted to the toilets that remain in use.