Fiberglass is fine for a holding tank, provided it is properly constructed... after all fiberglass boats have lasted many years...
That is reassuring.
Are there any special advantages to HDPE?
Is it possible to fabricate your own HDPE tanks?
Long flat tanks have a problem in that they'll be harder to empty completely. If you leave much waste sitting in the bottom for extended periods of time, it can eventually build up and reduce tank capacity. A taller, more vertically oriented tank is usually a better idea IMHO.
That is what I feared. So a flat tank in the floor under the bowl would probably not work well. To get the right verticality I might have to rip out the sink and redo the vanity so a holding tank can go inside the cabinet. I am not at all keen to lose the hanging locker to a holding tank.
If the tank inlet is high on the tank, as it should be, having the tank higher is probably a good idea, since it may allow you to gravity drain the holding tank.
I think I will have a macerator pump (a requirement in may areas where discharge is allowed) to pump out the tank. As I understand this pump is positioned after the Y valve on the overboard seacock outlet. i.e. pumpout stations have their own pump.
The vent line should be at lest 5/8", preferably 1", and as short and direct as possible to maximize oxygen getting into the tank. Anaerobic bacteria is the stuff that makes the tank stink... Aerobic bacteria are good...
The vent is clearly very important. If the vent is too small or too long the tank will be anaerobic (bad), but if the vent is not positioned far enough away from the cockpit it could stink (also bad).
Would it work to have a small diam and short run inlet vent and a longer larger diam vent running up the wind gen pole?
I guess I am concerned that for a very short vent there is a risk of waste coming out of the vent when it is full and the boat is in rough sees and heeled. I suppose it is important that the vent exit is high enough above the tank that this cannot happen. (Which makes my planned config difficult, since the locker where the tank could go would be very close )
Where do folks position the vent outlets?
Anyone regretted their vent or tank installations or thinking of changing them?
What about using an air inlet vent in combination with an air outlet and a small fan to force air through?
Can folks ever smell the tank when outside on a calm day?
I guess what I am saying is that if there is any smell from the tank, I would consider the installation a failure and certainly my wife would justifiably freak out! So no matter what the cost I cannot have a smelly tank. So if holding tanks do lead to unpleasant odors, perhaps a Lectrasan or some other processing tank might be needed. So I really need to know, do ALL holding tank installations stink or just badly vented tanks?
I like the Lavac, as it is almost bulletproof and generally uses less water than traditional designs.
Does it use enough water to keep things moving so to speak?