Three Misc. Plumbing Questions

[Midwilshire]

Moving forward with the plumbing system, and we have three questions for the board's collective wisdom....

1.  Should we have more water or more storage?  We just obtained a 100 gallon freshwater tank and a 100 gallon black/grey tank, and both will go in the bay amidships.  We already had what is now an extra 100 gallon tank, which we had planned on under putting under the master bed.  But now that we have the two tanks downstairs, we don't need the one upstairs.  So, in this situation, would it make more sense to carry an extra 100 gallons under the bed, knowing that we'd have to dump somewhere before we could use it, or should we keep it simple and store Gigi's extra shoes under the bed instead?

2.   Do we really need to vent the drain pipes for the sinks and shower to the roof when the black/grey tank is already directly vented to the roof?  Having trouble imagining a scenario where the tank vent would not be operative, but the drain line vents would be.

3.   Should our 120v, 12 gallon household water heater be placed near the water tanks?  Wed like to mount it out of the way in the old OTR compartment up front, instead of next to the tanks taking up precious space in the rear bay (only two bays in the MCI5).  But that would require a 20' round trip water line run and two more holes through the bulkhead.  Is there a compelling reason NOT to put it up front?

Thanks!

[Ed Hackenbruch]

 #1. store the shoes,(or something else), hauling an extra 840 lbs of water around all of the time will affect your mileage and you will find that with a little practice you can get by with what you have just fine.  #2. no, our 5A only has a tank vent and has worked fine for the 30 years that it has been converted.  #3.  Your choice, but the longer the run, the more heat will be lost from the water.

[Jriddle]

Here is my take

Question #1 I see no reason not to have 100 gal fresh water storage and 100 gal Gray/Black. That is how I set mine up. Make sure your plumb your gray water so you can bypass the tank if needed.

Question #2 I installed three vents. I'm sure others will chime in on how they only installed one with no problems. I have had no sewage smell while in motion or parked and I believe the vents have been the reason.

Question #3 You can mount the hot water tank where you want. The down side for me would be how long it takes to get hot water to the faucet wasting valuable water from the storage tank. I would mount the hot water tank near where it is going to be used.

[zubzub]

2.  venting has to do with the length of the run from fixture to main vent.  Basically you don't want a slug of water to pull the water out of the p trap. If the run is long running a higher  vent line to the main vent  will prevent this..or..I also like to use one way vents (spring loaded thing, can't remember what it is called right now, basically a vacuum for the drain line) when running a vent line is not practical.  This is all residential information but should apply to RV as the basics are the same.

[Handyjim]

My S/S RV uses the spring-loaded vents under kitchen and bathroom sinks, as well as a tank vent.  The under sink vents install on a short stub in the drain line.  I bought a replacement at Home Depot.  My guess is that's the way to go.

[belfert]

A lot of busnuts plumb in a valve or solenoid in the shower to return "cold" hot water back to the fresh water tank.  I decided not to do this as I have a lot of different friends on trips and they have enough trouble with the whole navy shower concept.

[Dave5Cs]

We have a 5C same as . No problems with one vent.No smells critcal distance is what Zub Zub was talking about which is length to the vent exit and a 1\4 inch higher than your center of trap to center of entry into the main stack pipe vent.Thats more for a house.You probably can not achieve that in a bus and really not nessary.

Dave5Cs from Galaxy S III

[bevans6]

Venting the fixtures and venting the tanks are two different questions.  You can certainly use air admittance valves at the sinks if they are a ways away from the tank, you can also vent the main drain line to the roof, and you should always vent the grey/black tank to the roof although many will now chime in and say you don't need to.  I say you do because the sewer gases are lighter than air and the vent run needs to be always rising, never horizontal or downward along it's run.  You can use the main drain line from the sinks as part of the tank vent to the roof and hit two birds with one stone.

I have a 100 gallon fresh and 100 gallon grey/black combined.  I would not have more fresh capacity than I had grey/black since you really don't want to overfill that one...  In fact I have never actually filled my fresh tank over half full, never felt I needed it.  Depends on how you plan your trips.

Brian

[Melbo]

I did my venting layout so that the tank vent is within 5 feet of all the traps. Then I did the wet vent thing so the traps drain into the vent stack. I have had no odor or venting issues.

The water heater should be closer to the kitchen sink (where you want hot water the soonest and the most often) When you take a shower you run the water long enough that the run doesn't matter and the vanity is used mostly for brushing teeth (cold water only).

The option of an extra 100 gallons of fresh water seems to me to be overkill BUT if I stayed where water quality could be of question then an extra 100 gallons of water of a known quality could be nice to have.

HTH YMMV

Melbo

[TomC]

1)-I have 130gal fresh, 85gal gray, 45gal black-enough to sit for a week with two people. On my truck will have 200gal fresh, 115gal gray, 65gal black-but it is also a 3ax truck.

2)-As to vents, it's nice to have a plumbed in vent going up from the drain just past the P trap. Then you won't drain the P trap from syphoning. You can just have a vent in the tank also. The trick is to add a bit of water to refill the P trap after you use the sink.

3)-On my bus, the run from the water heater to the shower is maybe 10ft and it takes about a count of 20 to warm up. On my truck it will be longer. As Belfert said, install warm up valves. I'm going to have one on the shower, bath sink, kitchen sink. The washer/dryer and dish washer doesn't need it. You can do anything as complicated as like what Sean has-electric solenoid valves on a switch (that also need maintenance periodically). I'm going to simply put a ball valve T'd into the hot water pipe before the regular valve plumbed back to the fresh water tank. Then to warm it up you just turn the ball valve on, put your hand on the valve until you feel it get warm, turn it off and get into the shower (or turn on the sink). Granted there probably will still be a few seconds of cold water, but I can't imagine it would be anymore then 5 seconds. A lot better then 20-30 seconds to warm up. Good Luck, TomC

[bobofthenorth]

There's not much sense having more fresh water than you have waste water storage unless as Mel suggested you plan to go to places where you don't want to use the water.  We carry 20 gallons of drinking water in a dedicated drinking water tank in addition to 100 gallons of fresh water.  When we bought the bus I thought that was a silly arrangement but I have grown to really appreciate it.  We can pick and choose when we take on drinking water and on occasion we refill that tank from blue bottles of purified water.  That allows us to be a lot less picky about what water goes into the fresh water tank.  

I would either mount the water heater as close as possible to the kitchen/head or install diverter valves to return the not-hot-yet water to the fresh tank.  It is unbelievably frustrating sitting out in the desert or anywhere else where water is precious and watching perfectly good water going down the drain while you wait for hot water to appear.  

[Len Silva]

In many places such as State Parks, you may have water available but no sewer.  If you have that use in mind, I would go for the largest waste tanks you can use.

[Midwilshire]

Gents, thanks for the helpful info and opinions!

1.  We're going to store shoes, not extra water.

2.  We're going to have only 1 vent from the black/grey tank to the roof.

3.  We're going to put the water heater up front and install the ball-valve recirculation system you guys described.

Thanks again!!

[belfert]

I find with human waste and toilet paper that a waste tank the same size as the the fresh water tank fills faster than the fresh water tank empties.

[John316]

Mid,

FWIW, we have 110 black and 200 grey water storage. We have about 100 fresh storage. We often end up on a two to one ratio. Mostly because we don't let the waste tanks get that full.

John