Inspection deckplates in holding tank?

[ferrailleur]

Is it a crazy idea to cut out the holding tank and install a deck plate in order to clean (shop vac) the bottom of the tank?
I know that it's not a pretty job but I'm in the cutting mood having added two deck plates to my Catalina 27 water tank...
The white water tank is polyethylene.
What's the black tank made of?
Any special adhesive sealant to be used on the black tank?
Thanks

[tkeithlu]

Sealed with an o-ring? Your major problem may be failure to seal, ergo smell or even leakage. include temperature expansion when thinking about that - is the tank vented?

[peghall]

Is it a crazy idea to cut out the holding tank and install a deck plate in order to clean (shop vac) the bottom of the tank?

Nope, not a crazy idea, but there's a a much easier way to flush out a waste tank without one: With the tank empty, add enough water to the tank via the pumpout fitting--'cuz that sends the water into the tank at the bottom to stir up any sludge--to cover the bottom to a depth of 4-5 inches...pump that out. Repeat...repeat...till you're pumping out clean water. Do it one more time and this time turn on any macerator pump to rinse it and any associated plumbing.

This should be done 2-3x season and especially in preparation for winter or other extended layup.


What's the black tank made of?
On a Catalina both your water and waste tanks are most likely the same rotomolded PE tank, made by Ronco Plastics 'cuz they've been Catalina's water and waste tank supplier for decades. Catalina just specs black as their holding tank color. (An yes, it's vented...USCG regs require that all waste tanks be vented to the outside of the boat because methane is flammable).

Any special adhesive sealant to be used on the black tank?
Nope...just the same rubber gasket that should have been supplied with the inspection ports you put on your water tank. Beckson has inspection ports with gaskets and threaded caps with rubber o-rings.


--Peggie

[a64pilot]

I would however get rid of the vinyl vent hose, if that thing doesn’t stink now I’d be surprised.

[peghall]

I totally missed that...Good catch!



--Peggie

[ferrailleur]

Originally Posted by peghall

Is it a crazy idea to cut out the holding tank and install a deck plate in order to clean (shop vac) the bottom of the tank?

Nope, not a crazy idea, but there's a a much easier way to flush out a waste tank without one: With the tank empty, add enough water to the tank via the pumpout fitting--'cuz that sends the water into the tank at the bottom to stir up any sludge--to cover the bottom to a depth of 4-5 inches...pump that out. Repeat...repeat...till you're pumping out clean water. Do it one more time and this time turn on any macerator pump to rinse it and any associated plumbing.

This should be done 2-3x season and especially in preparation for winter or other extended layup.


What's the black tank made of?
On a Catalina both your water and waste tanks are most likely the same rotomolded PE tank, made by Ronco Plastics 'cuz they've been Catalina's water and waste tank supplier for decades. Catalina just specs black as their holding tank color. (An yes, it's vented...USCG regs require that all waste tanks be vented to the outside of the boat because methane is flammable).

Any special adhesive sealant to be used on the black tank?
Nope...just the same rubber gasket that should have been supplied with the inspection ports you put on your water tank. Beckson has inspection ports with gaskets and threaded caps with rubber o-rings.


--Peggie

excellent answers... Thanks Peghall
will have some follow-up questions later.
Again THANKS

[ferrailleur]

Originally Posted by tkeithlu

Sealed with an o-ring? Your major problem may be failure to seal, ergo smell or even leakage. include temperature expansion when thinking about that - is the tank vented?

what about no gasket just good old 3M 5200 after clamping down the seal?
Thanks

[RossD]

I've had zero luck with sealants on PE tanks, for what it's worth.

[jen1722terry]

We have a 5" inspection plate in our holding tank, which is in the keel and otherwise difficult to inspect and repair. No leakage, but we're careful to get the plate screwed in properly and we change the O-ring every other year.

The plate was installed by the PO, but we'll need it one day for the holding tank on our '84 Cape Dory sometimes develop leaks. Thickened epoxy then has to be poured in and distributed over the bottom and lower sides of the tank to stop the leaks.

Ditto on the vent hose and maybe ensure there are no spider webs or other bugs blocking the outlet.

Great, versatile boat, the Catalina 27. I've seen so many over the years with happy owners at the helm.

[peghall]

The plate was installed by the PO, but we'll need it one day for the holding tank on our '84 Cape Dory sometimes develop leaks. Thickened epoxy then has to be poured in and distributed over the bottom and lower sides of the tank to stop the leaks.

Sounds like you have a metal holding tank. They were common in the '70 because no one realized then that urine is so corrosive that it eats through any metal, even 316 SS. It starts in a weld in seam or a fitting, typically in an average of about 5 years...gradually turning the bottom of the tank into a colander. By the late'80s, polyethylene became the recommended material for waste tanks. It really should be replaced with a top quality plastic tank which, from your description of its location, means another location will have to be found for it. I'll be glad to help you do that.



Replacing the "vent" thru-hull with an open bulkhead thru-hull will not only improve the ventilation in the tank, but also make it a lot easier to keep the vent line clear because it allows you to stick a hose nozzle against it to back flush it every time you wash the boat and/or pump out.


--Peggie