Basic Plumbing Question

LK23 · 04-07-2006, 03:22 PM

My Horizon has two roof vents, one for black water tank and one for grey water tank. Why do I need a plumbing vent under the bathroom sink?

LK23 · 04-07-2006, 03:22 PM

My Horizon has two roof vents, one for black water tank and one for grey water tank. Why do I need a plumbing vent under the bathroom sink?

AFChap · 04-07-2006, 03:43 PM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Why do I need a plumbing vent under the bathroom sink? </div></BLOCKQUOTE>
You don't ...but you DO need the vacuum break valves that are under both your bathroom and galley sinks. (as the replies pointed out on your similar discussion a few days ago). They are not vents ...they are designed to let air INTO the tanks to avoid a vacuum being created, NOT to allow air out ...the roof vents do the letting air out thing. If your vacuum break valves are allowing odors into the motorhome, they need their rubber valve cleaned, or perhaps they need to be replaced.

LK23 · 04-07-2006, 06:03 PM

OK, I understand now. One brings air in and the other lets air out. I have replaced the vent under the sink in the bath. I am now trying to understand why I am getting a odor when using the ceiling vent fans. I have posted questions on the RV 360 to see if that would resolve the problem.

olley · 04-08-2006, 04:49 AM

Hi I think there is a misunderstanding about air addmitance valves, they are fitted near to the trap to prevent a vacuum in the waste pipe as you empty the sink, sucking the water out of the trap (U bend) if this happened smells could then come up through the trap into the coach.

They need to be not only clean, but able to to move freely.

You can test them, by filling your sink up, let the water go and listen, as the bowl completely empties you should not hear a sucking sound from the waste.

If you do the same again but put your ear near the valve, and get someone to put the plug in as the bowl empties, you should hear the valve operate.

Olley

AFChap · 04-08-2006, 01:53 PM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">to prevent a vacuum in the waste pipe as you empty the sink, sucking the water out of the trap </div></BLOCKQUOTE>
I don't think we have that problem as we have never had odors inside the coach except from the rear roof vent while driving. However, when the wife pulls the drain plug on the galley sink I can hear "gurgling" in the shower & w/d drains. Does that indicate a vacuum breaker is not working properly? ...or perhaps the roof vent?

olley · 04-09-2006, 12:41 AM

Hi Afchap I would think your vent is blocked, as the water is rushing into your waste tank it cause's a small increase in pressure in the tank, which should be vented up the pipe, the gurgling you can here is this air coming up through the shower wastes. (I would think this would be smelly)

I would also think that if the vent is blocked that when you empty your tank this could pull the water from your traps, your air admittance valves are not designed to prevent this, that's what the vent is for, as its much larger, you are afterall draining your tank with 4" pipe.

Hope this helps.

Olley

AFChap · 04-09-2006, 09:09 PM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">I would think your vent is blocked, </div></BLOCKQUOTE>
That sounds logical, but we've never had any odors when we hear the gurgling drain pipes... I did check the vacuum break under the galley sink and it appears to be working properly.

Reckon how I determine if the roof vent is blocked? ...overfill the tank and see if it shoots liquid out the roof vent?? :0

olley · 04-10-2006, 05:05 AM

overfill the tank and see if it shoots liquid out the roof vent?? :0

That would do it

If you can remove the vent cap on the roof, fill the tank, climb on the roof and put your hand over the pipe as someone lets the water go, you should feel a fair bit of suction.

You could also put long bit of rigid cable trunking down the pipe, (or simular) and listen for it hitting the bottom of the tank. (make sure you don't lose it)

Just had another thought, I believe the vent pipe goes through a tank fitting, and then into the tank, if its been pushed into far, after the tank has filled up a bit, the liquid could cover the bottom of the vent pipe, maybe somebody else could confirm that or not.

Best of luck.

Olley

AFChap · 04-10-2006, 06:29 PM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">believe the vent pipe goes through a tank fitting, and then into the tank, if its been pushed into far, after the tank has filled up a bit, the liquid could cover the bottom of the vent pipe </div></BLOCKQUOTE>
Ahaaa!! ...so before I pursue the gurgling very far I'll want to determine if I hear it EVERY time she drains the galley sink, or if I hear it only when she drains the galley sink when the tank if close to full! That would be telling...

I hadn't thought of the "feel for suction" as the tank is dumped ...that might assist. I could feel for suction at the respective vents (first figuring out which is which) as the black tank is dumped, then as the gray is dumped, and compare what I feel to one another.