Fuel tanks, gas installation, plumbing and holding tanks

Fuel, gas, water and waste systems carry fire, explosion and health risks. Each one is checked for leaks, age, material and approved fittings.

Updated 24 Oct 2026 2 min read

Key points

Tank material. Stainless steel, aluminium, fibreglass or polyethylene each fail differently. Corrosion usually begins on the underside, where water collects.
Contamination. Draw a sample from the bottom. Water and black sludge show diesel bug, which clogs filters and kills engines in rough water.
Hoses and fittings. Fuel hoses should be of an approved fire-resistant type, and clamps should be stainless.
Valves and vents work and are clear.
Gauges read plausibly.

The gas bottles sit in a locker that is sealed from the boat and drains overboard.
A regulator and a shut-off valve (often electric) are fitted, and you can reach the shut-off from the galley.
Hoses carry a date and a replacement period. Old hoses crack.
Appliances such as the stove have flame failure devices.
A gas leak test shows the system holds pressure. Ask the surveyor to carry it out or witness one.

Smell at the heads, and in the lockers around the tank.
Sanitation hoses go brittle and absorb odours with age. Replacement is a normal job on boats over 10 years old.
Check the Y-valve, the macerator and the deck fitting for pump-out.
The rules on black water at anchor are strict in the Med. See Anchoring rules: Posidonia, marine reserves, buoy fields and black water.

Test the electric and manual pumps, the float switches, and the discharge outlets.

Gas and fuel faults are safety items and should be fixed before the boat goes to sea. See How to read a survey report and cost the findings.

Also useful at step 5 Seacocks, through-hulls and skin fittings

General information, not legal, tax or financial advice. Rules change; check your own case with a professional or ask us.