The holding tank in many boats is constructed of low density polyethylene, heat welded from flat sheet with polyethylene fittings. Not much can go wrong as polyethylene does not corrode, is impervious to odour and has great impact resistance.
The hose, however, is another matter and in many boats is multi-ply rubber with a spiral wire in the core to support tight bends. In the photograph (left), a cross section of this hose type is shown. The hose was cut from the discharge section from the head to the inlet of the holding tank. The hose looks great from outside but has deteriorated to a point that cracks in the rubber have allowed water (plus) to soak to the steel which has then rusted and expanded these cracks to destroy the integrity of the hose.
The new white hose, shown in both photos, is vinyl with a hard poly-vinyl spiral to provide support at bends. This hose is formulated to provide excellent resistance to odour penetration and should be far superior to any rubber material. However, it is difficult to install.
Procedure notes for hose replacement:
1. Note that all hose is 1.5″ inside diameter and all threaded fittings in these assemblies are classed as 1.5″ diameter.
2. Remove, clean and refit tank fittings (threaded) using teflon tape on the threads and assemble using hand torque only. Do NOT overtighten the threaded polyethylene fittings as a torn or stripped female thread on a tank fitting will generate problems that you do not wish to face. In the assembly photo, notice the white teflon tape is visible through the somewhat clear female tank fitting. Again, assemble these pieces as tightly as possible, by HAND ONLY.
3. Cut the hose pieces to length (using the old as reference) and assemble using new stainless steel clamps, doubled at sea and holding tank connections. DO NOT assemble the vinyl hose dry or with a lubricant such as soap (it just does not work). Instead, use a pan of very hot water. Soak the assembly end of the vinyl hose for 10 to 15 seconds and then assemble the vinyl hose to any fitting.
If your sanitary system needs an overhaul, do it now when your boat is out of the water. Work carefully – PATIENCE is the watchword as working in the recesses of your boat is difficult at the best of times. And once complete, another system is ready for years of trouble-free service.by Ed Sulis