Windjammer wrote:
Peggie,

I agree that this would not work for everyone, but it is not that bad an
idea. Many holding tanks would be capable of handling a small internal
pressure.

In my own case, the tank is solid fibreglass with a 1/2" well secured
"Starboard" cover. A calculation would have to be done on the cover because
it is the weakest part - It is well secured around the edge, but does span
about 30" in places. The fibreglass part of the tank is as strong as many
small boat hulls and well capable of handling some pressure.

My tank will self drain to about 1/3 full which leaves about 10" to
displace - this would take a pressure of about 0.36 psi to empty. I imagine
that many tanks see a higher vacuum than -0.36 psi when being pumped out, so
would probably handle this quite easily.

To do this, I could stuff a little putty or ?? into the vents, then use a
cheap air pump with a gauge to slightly pressurize using the pumpout
connection.

All this of course while offshore only!

Terry may or may not have been serious, but sometimes there are good ideas
that don't follow conventional practices. Keep an open mind - A system
designed to work this way would eliminate the need for a macerator pump -
one less expensive electrical item to go wrong.

GM



I'm very serious, except for the requirement to wear protective
gear. I take it you calculated your pressure requirement. I was
unable to measuer the pressure requirement with my tire gague, it's
so low.

I used plastic ball valves in the vent lines and a shraeder valve
"line flush adapter" RV accessory for the air connection, screwed
into an automotive radiator flush adapter. The first time, I used
wooden tapered plugs to seal the ventlines, another piece of
equipment every boater should carry.

The cost of a macerator pump is, of course, the main motivation.

Terry K