Waste and fresh water tank connection questions

[Merlin]

My next project (nearly the last) is to design and install the holding tanks.  As far as the design goes, I've agonized over it for the normally acceptable months.  The cut locations for the holes are now decided upon.  The questions I have are:

(1) What method of connection to the top of the waste tank is proper?  I have it in my mind that something flexible may be a good idea such as a flex coupling or even one of those pre-molded rubber elbows.  This of course requires a stainless steel clamp band and I do agonize about.  A band might slip afer I get the system all tucked away where it will be nearly impossible for me to reach it (easily).  I love to agonize!

(2)  The waste drain will be a 3" FIPT spun-in opening.  That is standard for the slice gate that I already have.  But ... I see that I will not be able to totally drain the tank since the fitting will be on the face of the tank, and not on the underside.  The colllar thickness of the spun-in fitting and thickness of the slice gate neck will keep about 7/8" of fluid in the tank.  Is this considered a problem since the tank will never be without at least some waste retained in it?  Maybe I can justify the retained waste as a "starter pool" for waste devouring organisms.

Gang ... hold my hand on this, my last big issue of agonizing.  I've labored alone on this bus conversion thing for far too many years to let anything small stop me now.  I'm saving a bunch of tiny "do it myself while full-time traveling" projects that will keep me happy for many years.  I want to be one of the crowd that is always working on something.

Merlin

[TomC]

I have 130gal fresh, 85gal gray, and 45gal black.  The black tank is designed with a slopping bottom that funnels into the 3 inch outlet allowing all it to drain fully every time.  The gray tank is a normal rectangular tank that doesn't drain, but isn't as important as the black to drain.  I too used rubber flex on the top.  I also agonized for a long time as to the installation of the tanks so to make getting them back out a relative cinch.  So far, after 13 years of being in, they haven't had to come out yet. You too should design the tanks so everything, including the vents and connections will be accessible since periodic tightenings are needed-vibration is a natural occurance on any vehicle.  Good Luck, TomC

[gumpy]

I used the rubber clamp on boots to connect my waste lines (sinks/shower and toilet) to the waste tanks. I had to stub up some ABS or PVC from the tank fittings and install the drains to nearly meet. Then install the rubber slip on boots and tighten the clamps. No problems with any of them yet. See my web page on installation of my tanks. I think it has photos of the boots. Available at Home Depot, Lowes, Menards, or any good building supply or plumbing house.

As for draining, mine gate valves are in the same position, about 1/2-3/4 inch above the bottom of the tank. It's never been a problem. Since I put my leveling system in, I raise the passenger side and lower the driver side and I get 99.9% of it drained. When I winterize, I end up with a bit of antifreeze in there anyway. Has never been a problem.

craig

[Melbo]

I used the rubber flex connectors too. I found that I liked the thinner rubber connectors with the stainless sleeve with the bands attached around them.

The thicker rubber connectors are what I usually use in most plumbing situations. I discovered that it is easy to slide a pipe in each end of those but in the bus my connections were so close that I had to slide the connector onto one pipe line the tanks up and then slide the connector past the joint. The heavy rubber connectors didn't want to slide very easily.

I then used the stainless wrapped connectors which have a thinner rubber connector. I could put the connector on one pipe and fold it back on itself and then align the pipes and unfold the connector onto the other pipe. I then simply installed the stainless band with the two clamps.

My holding tanks also do not drain completely so I simply add about a gallon of antifreeze and drive around a bit to get it mixed up before parking for the winter.

My fresh water tank does drain down so there is only about two or three tablespoons of water left because the 1/2 inch drain fitting is located close to the bottom and in a corner.

YMMV HTH

Melbo

[belfert]

See http://www.coastdistribution.com/PDF/CoastSiteFTP/Catalog/RV%20US/120_Plumbing/L416Plumbing_WasteLine_USA.pdf for what I used.  See the poly tank inlet or vent on the third page.  These are rubber fittings that slip into a hole cut in the tank and then your ABS/PVC pipe slips into that.  Any good RV dealer has these or can order from Coast Distribution.

These work great on poly tanks.  I even used a 3" one on the bottom of the tank (with lots of silicone) for my dump valve and it doesn't leak.  (I don't recommend for bottom or sides of tank if you can help it!)

Edit: fixed spelling

[Sam 4106]

Hi Merlin,
I, too, used the rubber couplings on all the connections to my waste tank (I have one combined black/ grey tank). As I remember it, the rubber coulpings fit so tight that they wouldn't leak even if the clamps became loose, since there is no pressure on them. Be sure the two pipes you are connecting are aligned and you will have no problems.
Good luck, Sam4106

[JackConrad]

We used a 100 gallon combination black/grey tank with the spin-weld 3" Female Pipe Thread (FPT) in the side as close to the bottom as possible. Yes, it does not drain completely, but 8 1/2 years later, never has been a problem.  If you drive the bus a little immediately before dumping, everything is stirrred up and if at least 3/4 full, the liquid carries the soilds out with it.  All the fittings in both of our tanks are spin-weld FPT (just different sizes). Our drain pipes connect to the holding tank using Ferncos ( there are available at the building supply stores and look like a short black rubber couple with a hose clamp on each end).  Jack

[rip]

When I had my tanks built,I had a fresh water line put in the opposite end on the tank so when I dump I can flush it out.After over five years of fulltiming it works great.
Don

[mikelutestanski]

Hello: 
   not to worry if the opening is not right on the bottom.  Has not been a problem for my bus on 10 years either.
   One possible solution if you have seperate black and grey tanks is to have a common outlet with valves on each tank and a final valve.  Then you can dump the black tank first then shuttle valves and let some grey water backfill into your black  tank  then reshuttle valves and let the black out again.. Then continue to empty gray after black tank is done and valve is closed.
   one possible solution of the many around. 
    I also used the uniseal fittings on top of the tanks .  You drill with a hole cutter insert the fitting  then grease the pipe and insert it into the fitting.  it is a real tite fit but works well no leakage in 10 years.  You can use them under water and the fittings will hold up under pressure.   remember a 2 foot high column of water will exert one pound of pressure.   
    Regards and happy bussing  mike

[Jerry Liebler]

Merlin,
    I built my tanks out of polypropylene sheets following "Gumpy's" excellent instructions.  All the openings in them are welded in FPT fittings (made by sawing  threaded polypropylene couplings in half).   I used PVC MPT adapters glued to short lengths of PVC pipe for all the 'top'  connections into the waste tank.  I used a "universal" coupling, which is a flexible plastic 'sleeve' clamped by 2 stainless clamps over a sheet of rippled stainless to couple to the PVC lines (drains and vent).  I got the couplings at the local Lowes.  Since I  built my own tanks I located the outlets so that the threads are in line with the bottom surface of the tank, actually the thread adapter is welded into the side of the tank with the bottom portion welded into the floor of the tank.  I did this to minimise the unusable capacity of my fresh tanks and minimise he undrainable quantity in my waste tank.  I have less than 1/4" of unusable in all my tanks.
Regards
Jerry 4107 1120 

[Merlin]

Thanks fellows.  I finally mustered the courage to order the tanks.  E-mailed my CAD drawings to Duracast.  When the tanks arrive, the fun starts.  If only I could train my cat to get in that tight bay and do the hook-ups !!

Merlin