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Posted: Wed Mar 04, 2009 10:14am

Post Subject: installing loo

I am having a loo with holding tank installed. The tank is under the bed at the stern. Where is the best place to have the outlet and breather? I would prefer the gunwhale as the position on the roof by the stern hatch door worries me. If it is there will be experience more unpleasant smells when we are on the cruiser deck?


Posted: Wed Mar 04, 2009 11:09am

Post Subject: installing loo

Dear Dale. I believe the shorter the pump out hose the better so I would fit the pump out connection on the gunwale. Depending on width of the catwalk you might have to file a flat on the flange so it sits against the cabin side weld, but make sure the pump out connector will not foul the cabin side. If the catwalk is narrow it will just have to go on the roof, but there should not be any smells because the pump out fitting normally has a cap on it. You do not mention a rinse fitting and I think they are vital. The rinse outlet into the tank should (in my view) be piped so as to wash anything on the base of the tank towards the pump out fitting. This may packing the tank slightly so the pump out is at the lowest point. If the boat trims down by the stern just make sure the pump out is at the back of the tank. The rinse can be either on the roof or the catwalk, but again it is normally capped so smell should not be a problem. If this is a vacuum toilet then the tank can not have a breather as such but will need a vacuum pump outlet. For the reasons I explain below I think you will always get a stench when this type of toilet is flushed - especially after it has not been used for a while. The breatherS (note plural) are vital on macerator and dump through holding tanks. If you kill the aerobic waste digesting bacteria by either using blue or by suffocating them then the waste will be digested by anaerobic bacteria and these are the ones that cause smell. So do not plan to use any additive that will kill the bugs and secondly ensure you have a free flow of air across the contents of the tank. I would suggest one large breather at each end of the tank. By large I mean larger than one inch id. I think I used 28mm copper. Unless the hull builder has or can weld pipe stubs into the hull you will have to use skin fittings which can have their heads scraped or knocked off, so fit these immediately under the top rubbing band and inspect them from time to time. Observe the minimum distance form the water line which is I think 10 inches for private boats, but check the Boat Safety Scheme regulations which are available form their website for download. Better still comply with the hire boat section. I made up a shallow metal box containing a computer fan which I fitted into one of the breather lines. This is controlled by a pneumatic timer light switch and provides positive venting while the deed is being done and for a while afterwards. I feel this is vital on a dump through toilet. If this is a macerator toilet ensure the pipe run between toilet and tank is run in such a way the waste can not pool in the pipe (see below). This typically involves a short vertical run from the toilet and then a long downhill to the tank. Finally, if smell is a concern, do not skimp on the cost of the hoses connected to the tank. Some can allow smells to permeate through the wall over time so quality is the way to minimise this. Tony Brooks

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