I try my hand at a bit of cut & paste from
the 1993 Thames Bylaws. That are on the Gov website.
Might be of interest
Use of vessels with sanitary appliances
66 (a) Subject to the provisions of paragraph (c) below no owner or master of any vessel shall keep or use or knowingly permit to be kept or used on the river any vessel provided with a sanitary appliance of such design that polluting matter normally passes or can pass into the river.
(b) Where any vessel is fitted with a sanitary appliance, such appliance shall be so designed, constructed and at all times maintained as necessary to prevent any such passage as aforesaid.
(c) The master of every vessel present on the river, at the date of coming into force of these Byelaws, and of every vessel on the river on or after such date, if such vessel is fitted with sanitary arrangements or appliances so designed or constructed as to permit the passage into the river of polluting matter, shall without undue delay give notice to the Lockkeeper at the lock nearest to the vessel’s point of entry to the river or to any Officer of the Authority specifying the nature of such arrangements aforesaid. The master shall also, upon being requested by such lockkeeper or other Officer of the Authority so to do, afford such Officer of the Authority facilities for the taking by him of such steps by way of sealing or otherwise as may be reasonably necessary for preventing the passage into the water of polluting matter from the vessel so long as the vessel remains on the river. So long as the vessel remains on the river, no interference or alteration shall be made with the sealing or other steps so taken as aforesaid except with the approval of the Authority.
(d) No person shall discharge polluting matter into the river from any vessel or from any sanitary appliance used thereon.