The Trophy Tax was levied every three years to defray the expense of raising the men to serve in the Militia of the City of London, plus incidental expenses such as accommodation for the militiamen.
As for Orphan Tax, Church Rates and Poors Rate these reflect the burden on each parish of looking after the poor. There is this on the pages of www.parliament.uk :
"The problem of poverty caused growing public concern during the early 19th century. The existing system for looking after those unable to care for themselves - the old, sick, disabled, orphans and unemployed - was based on a series of Acts of Parliament passed during the later Tudor period. These laws imposed an obligation on every parish to take care of its poor, though this had much less to do with compassion than with the need to preserve order and stability.
By the end of the 1790s there were clear signs that the system was under severe strain. Increasing numbers of parish poor were seeking assistance and the cost to ratepayers of maintaining the system was rising alarmingly, especially as payments were linked to the rising costs of bread and the size of families.
A parliamentary inquiry in 1777 noted that there were 1,916 workhouses in England which housed some 90,000 paupers."
Thames Water at One pound two shillings a year presumably covered the cost of drawing water from the Thames alongside One London Bridge (just imagine the pollution!) and Sewer Rate at £0/14/4 was paid even though in practice the premises were served by a cess pit constructed underneath the cellars. They leaked - often, judging by Richard's accounts! The tax would therefore have been over and above what he had to pay for "repairs to the Privy". In 1793 these amounted to over sixteen pounds ("jobb at the Privy, paid to Mr Poynder, plumber, for Grate at the Privy, Carpenter...ditto, case to lead pipe").
The year before Richard had paid out one guinea in support of "a petition to the Commissioners" asking for the sewers to be taken over at public expense but until that happened Richard would presumably have needed to avail himself of the services of a nightman - someone to come at night, when the shop was closed to customers and all good people were a-bed, in order to empty the overflowing cess pit by hand, using barrels. The procedure is set out on the handbill of one Richard Harper (courtesy of the British Museum).