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Attaching a drawing

Have you come across PO toilet systems having a separate flush water tank? Both tanks on same side of boat & of appropriate capacities. Boat ballasting done under "nominal" conditions. Boat will list when pumped out but should right when flush tank refilled. Like to send a diagram if poss. Thanks.

Asked by: Guy Campbell  | 6.12am, Wednesday 8 March

WW says:

The short answer (in my case) is 'No'. But if the main water tank straddles the centre line of the boat (which most do) and the much smaller holding tank is more or less on the centre line, there shouldn't be too much of a problem with listing. My own boat has both tanks on the centre line and stays level in all conditions.

Graham Booth  | 10.31AM, Wednesday 8 March

You can email me directly at mark.langley@waterwaysworld.com if that helps.
Seperate flush tanks are common on cassette toilet systems; some seagoing craft do, but mainly to separate out drinking water from toilet flushing water (a requirement in some jurisdictions- not in the UK!).
More commonly twin holding tanks are used to trim ballast, which can work out more cost-effective (and also better for balancing trim, as the tanks can fill equally)

Mark Langley  | 1.07PM, Wednesday 8 March

Your idea is certainly novel but does involve an extra tank. As Graham says, careful positioning of the tanks can alleviate or dispel the listing from a poorly located toilet tank.
If your layout necessitates an off centre toilet tank, a similarly positioned flushing tank would only alleviate, not eliminate a developing list as it empties; this is due to the fact that most of the contents of the holding tank comes from the users, with flushing water being only a small proportion. Boat toilets use much less flushing water than the domestic variety because they discharge into a limited volume tank.

Rupert Smedley  | 1.21PM, Wednesday 8 March

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