Originally Posted by rebel heart
... What I'm wondering about is:
- What kind of fitting do I install in the hole I drill? I know it's not a thru-hull, or should it be, even though it's above the waterline?
- How do I bed this fitting into the hole?
- Anything else I'm missing?
Install a Vent Fitting, such as pictured below (not a clamshell cap).
The vent is installed above the heeled waterline, and does NOT require a seacock.
Toilet intake and overboard discharge lines should be equipped with seacocks (valves) to stop the inflow of seawater in the event of a hose failure. A seacock is operated by a lever-type handle that gives clear indication whether the valve is open or closed. These seacocks should be readily accessible for maintenance and oriented so that their handles are easy to operate.
When drilling, maintain a relatively slow drill speed, and advance the drill bit very slowly. Let the drill bit do all the work. Where practical, use a hole saw, or a shallow angle tip drill bit.
Seal the raw exposed fibreglass edges of the hole with epoxy resin. All FRP working tends to leave a rough, shattered or chipped edge, where water
can penetrate into the laminate.
I like to chamfer (countersink a conical recess) the outside surface of holes. This relieves the stress on the gellcoat, mitigating cracking. The chamfer also provides a cavity (think o-ring) for the sealant
to bed the fitting.
Bed the fitting with a flexible polyurethane sealant
, such as 3M ď5200" or ď4200". Donít use silicone. Prior to installation
, clean the hull
area and fitting, ensuring no wax, oil
, or release agents remain to contaminate the bond joint.
The holding tank vent fitting should be located above the holding tank, and above the waterline (at all angles of heel). It should also be no less than 24 inches away from any opening (hatch/portlight) into an accommodation space.
Ensure that the holding tank vent line has a constant rise from the top of the tank to the vent fitting. Otherwise low spots may fill with sewage and act as a "U" trap, effectively plugging the vent. Avoid bends, as far as practicable.
Vent line should be as short as possible.
If fitting is to be located in hull
topsides, select a protected spot where it will not be subject to damage from pilings, etc.
Keep vent fitting opening(s) free of corrosion
, insect nests or other material that may result in a clogged vent line. If the vent pipe is not clear, it is possible to build up pressure in the tank and either rupture the tank or blow the hoses off. Do not use the cheap
clear vinyl tubing; but rather a high grade, thick wall, reinforced tubing. All tubing should be opaque. Letting sunlight get into the lines allows the algae to grow that can cause a most unpleasant odor