Sewage and Waste Water

MCA MGN 599 Amendment 1 explains that the UK sewage certification and equipment provisions it describes apply to ships on international voyages over 400 gross tonnage, or smaller ships certified to carry more than 15 people. It also states that those regulations make no specific sewage provisions for vessels below both thresholds. That distinction matters: the large-ship MARPOL discharge table must not be presented as though every small yacht has the same legal equipment regime.

The same MCA guidance gives clear best practice for smaller pleasure vessels. Return waste to shore where possible; use a holding tank if fitted and empty it at a pump-out station. If shore disposal is impractical, its UK advice is to empty a holding tank only more than 3 nautical miles offshore in open sea where dispersion is effective. A boat without a holding tank should avoid toilet use in poorly flushed estuaries, inland waterways, inlets and crowded anchorages by using shore facilities wherever possible.

That is a UK small-vessel baseline, not a worldwide permission. Harbours, inland waterways, protected waters and other countries can prohibit or more tightly control overboard discharge. Before departure, trace the valves, label the holding-tank positions, check capacity and pump-out availability, and make sure the crew cannot accidentally select an overboard route in restricted water.