Peter Grabow’s request for information on sealant for the polyethylene tanks came just as I was about to ask the very same guestions. The sealant I have is 4000 marine and the fittings are not marelon but schedule 40 and 80 and stainless steel reducer for the vent line. My question is that acceptable for a holding tank? Or should I get Marelon fittings and use something else for sealant?
Thanks,
Brian Cayer
Spirit~Wind
N30U 419
Westbrook, Ct
Hi,
As previously mentioned, I believe the correct sealant to use is 3M 4200 or Silkaflex 291, don’t use silicone or Teflon tape. Unless your tube of 4000 is pretty new, I’d buy a new tube given this is a somewhat mission critical application, at least the holding tank is. My boat has both Marelon and Sch 40/80 fittings. Ronco says not to use metal fitting directly on the tank.
Here is link to Ronco’s website info on…
Pre-installation tank cleaning: https://ronco-plastics.com/sanitation-info/
Insallation: https://ronco-plastics.com/installation-info/
You may also want to visit the Marelon website to see what sealant they recommend. There are some instances where some sealants are not compatible with certain plastics.
Cheers,
Don
’87 NS30U #369 - Breezin’
Vancouver, BC
Schedule 40/80 PVC? We’ve probably got that all over our boats, but I’d stay away from PVC on the holding tank. PVC becomes brittle when cold and can crack from stress or vibration. Even the thermal expansion and contraction of tightly restrained piping or tank could stress it enough to crack it. I know this through painful personal experience, not just some vague theory of mine. It’s not a really high probability, but if that happens while you are laid up for the winter you won’t know until you get some stinkwater in the bilge. And the broken fitting will be glued in with 4200. Then you’ll really wish you’d used Marelon.
Brian Godfrey
Your are right, I had a Sch 40/80 vent fitting on holding tank crack. Luckily it was easy to fix, I replaced it with nylon fitting and 4200. Holding tank discharge also Sch 40/80 was weeping a bit, previously installed with Teflon tape. I replaced it with Marlon fitting and 3M 4200.
Don
Hi Don,
Thank you for your input and the links for the pre and installation guides from Ronco. Very helpful!
Now, if the 25-35kt winds would subside, and the temps would remain in the 60’s around here, I can get to work!
Regards,
Peter Grabow