What sealant for water tanks?

[Kelkara]

I decided to open up my water tank to give it a thorough clean ...

my question is ... what sealant should I use when I screw the top back down? The present stuff is translucent pale brown and elasticcy.

[Putt-Putt]

A cork/rubber gasket. Canadian Tire, Automotive section, about 18' x 36" x 1/16" thick. $20.00+/- It must be made in one piece, so size matters.

It's rolled up so unroll it and let it relax for 24 hours, use the lid for a template, and drill all the fastener holes first through the holes in the lid, sightly smaller than the outside diameter of the fasteners. Next cut the inside and outside to size so that the gasket is just the same width as the overlap of the lid on the tank. Standard scissors are fine, it's easy, all done in about half an hour.

No sealant required if the lid fits tight to the tank. You have lots of fasteners so this is almost assured. No need to over tighten the fasteners.

If you want, a really light coating of Permatex Silver Anti Seize (Canadian Tire $12.00 for a lifetime supply) on the gasket will ensure that the next time you remove the lid the gasket remains serviceable. Olive oil as a substitute may only last a year or two.

You will thank me after the next opening of the lid as there will be nothing to clean in order to reassemble.

Clean the sealant off of everything first, in my world sealants are not fit for this kind of service where disassembly is required.

[Matt Johnson]

We used Sika 1A on our previous boat's water tanks. It is certified to the NSF/ANSI Standard 61 for potable water.

Matt

[Celestialsailor]

Personally, I wouldn't hesitate to use good ol' Silicone Seal.

[Rumrace]

Lexel or a very unusual food safe silicone. The tank is likely PETG and almost nothing adheres to it.

[Celestialsailor]

The tank appears to be glassed into the hull.

[Kelkara]

Thanks everyone ... yes tank is glassed in.

I managed to get some "aquarium grade" silicone which is rated safe for food contact, and seems to be doing the job.

The rubber gasket idea sounds good ... if it looks like I'll make a habit of opening the tanks I'll try that next time.

[Cwens]

Originally Posted by Putt-Putt

[...] Permatex Silver Anti Seize [...]

I'd be very much disinclined to put that stuff in my drinking water.



MSDS: https://www.permatex.com/wp-content/.../sds/81464.pdf

[Rumrace]

Water tanks are not that expensive. Seems they all eventually expire. I’d be so disappointed it’s glassed in I’d sell the boat.
Uncle ALS fish tank sealant is amazing stuff. Most silicone struggle to adhere to glass. It’s not designed to hold onto ABS or PETG but will for awhile. Any glue which will adhere to PETG will dissolve it. Heat bonding can thin another area for the next break. You could use a flexible bladder.
Apparently most of our plastic things we eat drink and store food in is PETG.

[GordMay]

Polyethylene terephthalate glycol, or PETG, is a Glycol Modified version of Polyethylene Terephthalate (PET). There are several variations of this material, including PETE, and PETT.
PETG is less brittle, and more pliable than PET, making it ideal for bottles. It also has better shock resistance, and is better suited to higher temperatures. PETG is commonly used in 3D printing.
Silicone Adhesives, Cyanoacrylate (Superglue), Polyurethane Glue, Epoxy, and solvent welding all work well for bonding PETG.

[rslifkin]

Originally Posted by Rumrace

Water tanks are not that expensive. Seems they all eventually expire. I’d be so disappointed it’s glassed in I’d sell the boat.

Depends on what the tank is made of. If it's entirely made of fiberglass, it can be repaired, re-coated on the inside, etc. if there's an issue. Total replacement is unlikely.

[s/v Jedi]

Originally Posted by Rumrace

Water tanks are not that expensive. Seems they all eventually expire. I’d be so disappointed it’s glassed in I’d sell the boat.
Uncle ALS fish tank sealant is amazing stuff. Most silicone struggle to adhere to glass. It’s not designed to hold onto ABS or PETG but will for awhile. Any glue which will adhere to PETG will dissolve it. Heat bonding can thin another area for the next break. You could use a flexible bladder.
Apparently most of our plastic things we eat drink and store food in is PETG.

I hope not… my hull is part of the tanks and replacing wouldn’t really work for me.