We have a common toilet in our block and I’d be reluctant to remove it. We recently had a tradie crew on site for 8 weeks and they were working in dusty, dirty areas of the property – I wouldn’t have wanted them using the toilet in my apartment.
You never know when you’re going to need a crew on site for a lengthy period – replacing the roof, the lift, rendering – all lengthy jobs. I suggest keeping the toilet and taking a photograph before and after any use by the belligerent lot owners so that there is evidence of who has caused any damage. You could create a by-law to the effect that damage to the toilet and it’s little room is to be paid for by whichever lot requests that the toilet is unlocked for their tradespeople. That might make your belligerent lot owners think twice about requesting that the toilet is unlocked for their tradies. Might be less of a “sport” if they know they will be held financially responsible for any damage during the period of access. And “responsible” can include both a fee to correct any damage (eg. blocked toilet) or a cleaning fee if it’s left soiled.