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Originally Posted by PA BAMBI II
I am getting ready to start planning out my gray holding tanks (will be custom aluminum tanks) and plumbing my one and only sink. Several questions I am struggling with and hope to gain some insight from our awesome membership:
1) Due to massive space constraints under the floor of the Bambi II (small cavities/angle iron cross member connectors running the center/length of the trailer), I plan to tie together 2-3 smaller tanks with rubber couplings. Does each tank need to be vented, or just the one nearest the exit drain towards the release valve?
2) Can the sink vent be "looped" down through the floor/bellypan? I do not have easy access to a roof vent stack nor a clean way to install one. If not a looped system, can it go through the side of the trailer? How high does it need to be? Above water line/nearly to the top of the sink or must it just higher than the trap (Hepvo in my instance)
3) Can sink vent line be smaller than 2" plumbing pipe? Could PEX be used? (easier to work with/smaller, etc.)
Thanks for any insight. I built the interior/cabinets to fit our needs and we are very happy with them, but I am afraid it has made planning the plumbing more difficult. Kind of like putting the cart before the horse, but we wanted to get it up and running and have been camping without plumbing as it is a non-necessity. Now it is time to get it figured out.
Thanks!! Ben
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First understand the purpose of vents. From the waste tanks a vent lets methane gas (sewer odor) vent out. This vent also admits air into the tank when the tank is dumped. The smaller the vent the slower the tank will drain. At a fixture (sink drain, shower drain) air has to be admitted so that a vacuum is not created. At a sink a vent is not needed, but a vent is an optional way to admit air.
If you use multiple tanks you will need some type of vent from the top of each tank to allow air to escape when liquid builds up to the top of the outlet pipe. If the air can't escape liquid cannot fill the tank. The tank vent stack should go upward through the roof so that methane gas (odor) can be dispersed into the atmosphere. If a vent exits the trailer low on a side odor will be noticeable.
A vent is not required at each fixture. (Google air admittance valve). An air admittance valve is the proper solution when a vent is not available. At a sink, an air admittance valve should be placed as high as possible beneath the counter top where the sink is mounted.
I suggest that a tank vent should not be smaller than 1 1/2" pipe (though theoretically any size could work). Vents for multiple tanks can be tied together so that only one vent penetrates the roof.