If I recall, one major purpose of the vent is that when the holding tank is pumped out the vacuum pressure of the pumpout does not collapse the tank. Maybe you are talking about something else, but the pumpout stations around here make my holding tank moan and groan from the vacuum pressure being applied. DHS Duluth ************ On Mon, 11 Feb 2008 19:59:59 -0500 Steve Sipe <scsipe@comcast.net> writes: > Scott H.E. Welch wrote: > > "Brent Hodges" <vbhodges@gmail.com> writes: > > > >> Any one know of a convincing reason to add the vented loop to > this outlet? > >> Peggy, care to comment? > >> > > > > There is no need for a vented loop because a back-siphon could not > sink the > > boat -- all it could do is fill the holding tank. And even that's > not > > possible, because the pump has two one-way valves. > > > > Scott Welch > > > > > I dealt with the same question when I re-did the plumbing system on > > Maerin. I considered eliminating the vented loop between the > discharge > from the pump and the thru-hull. I kept it. Yes, at first blush it > seems > that the worst that could happen would be the tank filling with > seawater, but the function of the vented loop is a safety factor. > When > things go wrong, it's usually a progression of events that would > ordinarily not all happen at the same time, but for some reason, > well, > things go wrong. The vented loop is one more safety factor, so I'll > keep it! > > Steve Sipe > 4303 Solo "Maerin" > _______________________________________________ > http://lists.samurai.com/mailman/listinfo/trawlers-and-trawlering > > To unsubscribe or modify your subscription options (get password, > change email address, etc) go to: > http://lists.samurai.com/mailman/options/trawlers-and-trawlering > > Trawlers & Trawlering and T&T are trademarks of Water World > Productions. Unauthorized use is prohibited.

David H Sorenson <davidsorenson@juno.com> writes: >If I recall, one major purpose of the vent is that when the holding tank >is pumped out the vacuum pressure of the pumpout does not collapse the >tank. Maybe you are talking about something else, but the pumpout >stations around here make my holding tank moan and groan from the vacuum >pressure being applied. This is an excellent point. In fact, it's best to have not one but two vents, at least 1" diameter, with the outlets on opposite sides of the vessel. This will promote airflow through the tank and help with aerobic decomposition. By the way don't make the mistake I did and install the vent hose with low points. This will cause a buildup of water (from rain and or condensation) and will have the same effect as a P-trap under a sink. The vent lines need to be run in a continuous upward slope. However, the "vented loop" will not help with this. Scott Welch FirstClass Product Manager www.firstclass.com Those who make no mistakes rarely make anything.

Thanks to all for the comments / suggestions on the vented loop on my discharge pump. I have decided to go ahead and install the loop. I still don't think that with the type of toilets a backflow into the boat is possible, but barring a failure in the loop, it can't hurt. Might help with a survey somewhere down the road too. Brent Hodges "Brent Hodges" <vbhodges@gmail.com> writes: >> >> Any one know of a convincing reason to add the vented loop to >> this outlet? >> >> Peggy, care to comment?