Anti-siphon or not

[Al Dente]

I am doing a total rebuild of the black water system so I have a functional and practical holding tank system. I have even got the Headmistress's book and digested the contents[emoji6].
The discharge to sea from the blackwater tank will be as recommended: a pipe exiting the top of the tank going down to its bottom.
It will bend to the pump, then down to a valve followed by the Y to join the direct heads discharge then out the through-hull.
All the literature specifies an anti-siphon for this pipe. Why?

The valve will only be opened for a discharge of the black water tank at sea, then closed. You would obviously only do this in a quiet sea.....you will have left port in good conditions so it would not be long. Putting in this anti-siphon will mean 2 anti-siphons for the heads system unless all heads discharge goes via the holding tank; a practice I would regard as sub-standard. Only use the thing when you really have to; there is a risk of smells, forgetting it is in use etc.
Is this issue a pure regulatory issue or am I missing something?

[peghall]

If the top of the tank is well above the waterline and if you can mount the pump at or above the top of the tank, you can get away without the vented loop...provided the seacock is ONLY opened to dump the tank. If even one of those conditions can't be met, you need one.

If you do have install a loop, you can avoid a y-valve in the tank discharge line by putting a second discharge port in the tank--which is actually very easy, thanks to li'l gadget called the Uniseal--and so is making another pickup tube for it.

If you want to discuss it in more detail than is practical in open forum, send me a PM....I'll be glad to help you. And btw, hope you're finding my book useful!

Peggie
"If you can't explain it to a six year old, you don't completely understand it yourself." --Albert Einstein
http://www.amazon.com/New-Get-Rid-Bo...dp/1892399784/

[KISS]

OT, but...

Consider dispensing with the entire traditional head, and going to a desiccating/composting head.

Waste disposal need not be complex.

FWIW...

https://raindogps34.wordpress.com/head-project/

https://raindogps34.wordpress.com/20...ur-dry-toilet/