The 'approved' toilets are available 24/7 near to the 'letter box' where one can post the discounted landing fee.
That's something that I never ever remember to do (post the discounted landing fee that is). All those trips into YBHI over the years and I still walk right past the 'letter box'. The un-discounted fee usually turns up in the mail about a fortnight later. "FFS, forgot it again!".