[Public-List] Holding tanks

[Don Lang]

When using schedule 40 PVC slip joints its very important to ensure the joint is clean and to use an apropriate primer.
When I was the mechanical foreman at Queenship Yacht works we built 74 foot production yachts and 97 foot custom yachts.
We used schedule 40 PVC for many of the systems and we used schedule 80 CPVC for the chilled water systems.
The only failures we had  in the schedule 40 PVC slip joints were those that we improperly prep'd (most often the technician forgot the primer).
The threaded fittings (both schedule 40 PVC and schedule 80 CPVC) had a higher failure rate caused by technicians over tightening 
the threaded fittings, even the old hands would over tighten a fitting from time to time. None of the threaded fittings failed immediately but only after being subjected to days or weeks of service. (vibration)
In either system great care must be taken during assembly to ensure a satisfactory, trouble free joint.
If the joint is correctly assemble it can withstand the flexing and vibration associated with boating.
It has been used for more than ten years in large yacht construction and decades in the RV industry with the vehicles rumbling and rolling along the nations highways and back roads.
When I was the plumbing foreman at Bradford Grand Bahama we used an additional step of prepping the PVC joint  with a PVC cleaner, then primer, then cement.
We had a zero failure rate of our fittings.

Below is a good source for those looking for holding tanks.
They will drop ship from the factory to you.
Tanks are seamless, roto-molded, 3/8" thick polyethylene, good for sewage or water.
They will locate the fittings wherever you want them.
Odd shaped tanks: http://www.marinesan.com/comersus/store/catalog/07%20Tanks/TANKS,%20ODD.pdf
Bow tanks: http://www.marinesan.com/comersus/store/catalog/07%20Tanks/TANKS,%20BOW.pdf
Rectangular tanks: http://www.marinesan.com/comersus/store/catalog/07%20Tanks/TANK,%20RECTANGLE%203-8.pdf
General information: http://www.marinesan.com/holdingtanks.htm

Cheers, Don (#473)




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I have found schedule 40 and glue joints also act up.  I prefer schedule 80 with threaded connections.  As to maralon 1 1/2 hose barbs, they are not tight enough a fit.  For sanitation you want to have to soften the hose (heat gun, hair dryer or boiling water) to insure a leak proof joint.  Minor weepage is almost acceptable with a sea water connection.  Sewage weepage on the other hand..............
I will add that the entire rig must remain flexible.  A holding tank set up using all pipe will suffer from vibration and flexing. 


Jim Davis
S/V Isa Lei
CT35

"If everyone is thinking alike, someone isn't thinking."
George S. Patton








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