Holding tank inspection port

[Geek_Guy]

This is a sweet deal.

I've had mystery smells since purchasing this boat last year. Just looked at the holding tank and found someone had installed an inspection port. But it appears that they just tried to screw it on with lots of caulk. When the tank is full it runs black water out.

So my question is how to get a solid install and/or just put a solid piece on. My thought is that I would need some sort of backing plate with bolts through it and the tank because the tank is bowed. But I always get some sage advice from you guys...

Thanks

Dave

[tkeithlu]

The core problem is the curved surface of the tank. That screw down port requires a flat surface. So, if you want a port there the first step will be to remove the mess and then mount that port or a similar one on a wedgethat fits, without screwing it down. Once it has hardened, then you can use through bolts to strengthen the installation against your turning the plug. You don't want to create a situation in which the bolts force the frame of the port into a curve, because then either the threads will not engage or it will leak. Ordinary Bondo (fiberglass resin and fiber) would make the wedge. Backing could be limited to washers - it's not a high pressure situation.

Be surre that there is a good 0-ring around the plug - otherwise, it will leak/smell for sure.

If you don't want a port there, clean it off and then see if a sheet of aluminum will fit the curve of the tank - it might be a compound curve, in which case you'll have the same basic problem as with the port. Build a flat platform and then bolt it down.

I'm not wild about that sort of port in a black water tank. Those ports are mostly for ordinarry access through decks, not tanks. But then, an alternative doesn't come to mind.

Good luck with it.

[Geek_Guy]

I don't like the port there. I was thinking that if I can get a stiff cover(like you said aluminum piece, or something similar)and a backing plate under the top of the tank. Then bolts through the two with the tank sandwiched between would straighten the tank and create a solid seal. Also likely would need a gasket under the top piece.

Do you think that would work?

[Calif.Ted]

Could replace the tank, it's probably a Ronco tank, if so there should be a model number molded into the tank. What could someone possibly be looking for inside a holding tank, I know what they'd find and it isn't pretty.
https://ronco-plastics.com/product/w...-holding-tank/

[Cheechako]

Aluminum is not great with septic waste.
I guess you could make a round plate from fiberglass, or from poly like the tank but thicker. Then have many fastening screws (maybe twice what are there?) Clean it up well and use 5200 to put the plate permanently on there. Screw it down not too tight, let the 5200 set up for a day then screw it down a bit tighter.

If readily removed, just get a new tank.

[motion30]

stainless steel screws will corrode and give up inside a holding tank. Perhaps brass or bronze will last longer

[tkeithlu]

If you cover it with a plate you've got really only two ways to squeeze the goo - mount bolts from underneath before you put the plate in place or use sheet metal screws from above into the plastic - that's probably the way the port was installed in the first place. If you want to be able to remove it, use silicone ("30 year" has less water and shrinks less). I have two such aluminum plates on my 300 gallon tanks - I needed to get baffle balls into them - with 3M 5200 as the goo. No problems in 10 years.

[peghall]

I would remove the plate and clean ALL the goo off the tank and the plate. If that is curved, I'd cover the hole with some kind of rigid but flexible (if that makes any sense) material, seal the edges with a thick rubber gasket (rubber gasket material is available from big box stores, and secure it with bronze screws through the gasket.


If you still want an inspection port, Defender has 6" Beckson inspection ports that are designed to be installed in a flat surface using screws and a gasket. No sealant needed. No mention of an o-ring on the cap but one is needed and, because rubber dries out and cracks, will prob'ly require replacement about every 5-6 years.


--Peggie

[Mike Banks]

That is an inspection port for a closed space, certainly not a tank fitting.

[mitiempo]

Originally Posted by Mike Banks

That is an inspection port for a closed space, certainly not a tank fitting.

I agree. They are not built to keep liquids in a compartment or tank.

This is what you want - expensive but they work.

https://www.amazon.ca/Whale-Waterpro.../dp/B01NBK97L7

[Emouchet]

I have installed one of those on my diesel tank.
Will work fine I think on the Poop tank too:. Albeit a bit expensive may be:
https://www.seabuilt.com/

[thinwater]

Really, there are several problems:

• Ports should be on the centerline of the tank, centered fore-aft. Any other position they are subject to surging impacts and liquid when heeling. Common problem on tankers. ALWAYS put the hatch in the middle.
• Wrong sealant and wrong prep. There are polyurethanes that will bond pretty well to polyethylene, but you need to clean and sand, and then flame-treat (Google it) both surfaces. This makes a HUGE difference. Sika 291 and Locktite PLS40 are two of the best. 3M products do poorly on PE, as does silicone. A neoprene foam gasket would probably work well too.
• Inside backer. Cut a rigid backing plate, drill the holes, then cut it in half to insert. Tighten bolts through the hole. This is how diesel hatches are bolted in.
• And yes, a better hatch would help. These always leak. Normally a lot.

This can be done. I've done it countless times on PE chemical tanks. But too many mistakes were made.

[peghall]

I learn something just about every time you post! A question, however...


Most production boat builders seem to like positioning holding tanks to lie along the hull...and owners of those boats--sail as well as power--often want to install inspection ports. Since most of these tanks are less than 30 gal, how much impact would heeling actually have? And does how full the tank is matter?



--Peggie

[David Mathis]

A new tank would be a better fix than trying to seal a cover against a concave surface. Unless it’s a custom design specific to your boat, plastic holding tanks are reasonably priced.

[thinwater]

Originally Posted by peghall

I learn something just about every time you post! A question, however...

Most production boat builders seem to like positioning holding tanks to lie along the hull...and owners of those boats--sail as well as power--often want to install inspection ports. Since most of these tanks are less than 30 gal, how much impact would heeling actually have? And does how full the tank is matter?

--Peggie

All good points.

The answer would be no tiny tanks (12 gallons is kind of an insult to good sense) and good factory ports. I always try very hard to avoid filling past about 70%, to reduce the risk of not being able to flush, and to keep from clogging the vent.

The vent should be on the center line as well, but often it is in a corner.

----

Slightly off topic, but perhaps illustrative:

Major gasoline companies retire their tankers fairly young. They like to keep good equipment. They have 4-5 compartments, for each of the fuel grades, each with a hatch dead center. So far, so good.

Discount fuel haulers buy them, down rate the inspections to diesel and heavy oils only, and then cut the baffles through to make it into one big compartment. This means the 3-4 extra hatches are no longer in the center.

I have seen dozens blow either the forward hatch (braking) or the back hatch (steep hill), in each case resulting in ~ 500-1000 gallons spilled. A big mess, often coating the whole side of a hill (it runs and spreads). I remember throwing bags of absorbent down a hill, and watching them slide more than 200 feet (lube oil). I also recall a motorcyclist that ignored the cones and tried to drive up the oiled lane, sort of a slow motion disaster.

The right answer is to remove all but the center hatch, and replace them with solid plates. You maintain access for periodic cleaning and inspection, but you will have to turn more bolts.