black water tank replacement

[Fixit]

270 islander - I've got a cracked spin weld fitting in the top of my groco black water tank, makes for some stanky smells in the boat.

the macerator pumps works really well, but I likely need to replace the sani hoses. Is there anyway to repair a cracked spin weld fitting in the top of the tank or do I replace it?

im sort of leaning towards getting a custom hard plastic welded tank made, increasing its capacity and going to a jabsco macerator pump. anyone have any recommendations for a good tank level sensor? or have you done a similar refit of this shitank?

 

[SkunkBoat]

This works great as a monitor
https://www.greatgrady.com/threads/scad-tank-level-monitor.36326/

 

[DennisG01]

Can you pop a screw-out pie plate in the top and then use a bulkhead fitting? Cap/plug/burn/melt/etc the existing one and don't use it anymore.

"How" is it cracked? You could try plastic-welding to fix the existing fitting.

 

[SkunkBoat]

you might find some useful info in this thread too
https://www.greatgrady.com/threads/...erator-retrofit-265-express.19049/post-249233

Not sure what is cracked /how its cracked. Is it the inlet, pumpout outlet, macerator outlet, or the sensor fitting?
The Groco assembly can be removed and fittings plugged/wiring sealed and the plate reused to seal the top of the tank.

At the end of last season I waited too long and all of the on-water pumpout stations were closed. I had to jump in a Jabsco macerator and pump overboard before pulling the boat.
A spring project will be adding a valve and permanently installing the Jabcso. It will be much like what was done in the other thread.

I already have the SCAD sensor on the tank and it works great.

Removing the tank itself on my 265 was going to involve cutting and replacing some hoses. They are in great shape but will not come off.
I removed the groco macerator from the plate. https://www.greatgrady.com/threads/265-express-sanitation-hoses.36096/post-251916

All of that work was painful with arms and chest leaning into a hole.. good luck....

 

[DennisG01]

The Groco assembly can be removed and fittings plugged/wiring sealed and the plate reused to seal the top of the tank.

Oh, right. Your boats use a tank with an internal macerator. Disregard my comment about needing the pie plate.

 

[Fixit]

This is the groco shipt tank
The spin weld fitting for the level sensor has popped on one side. The sensor doesn’t work anyways. I’ll look into the scad units. But I was thinking I need a bulkhead fitting that’s solid ( no hole) to dis that. Or should I try plastic welding? Would a butane torch work well for this?

 

[Wild blue]

I’d replace it with a bulkhead fitting, unfortunately this would require pulling the pump as well but it would remain serviceable for the next time you have to work on the tank. Seems like the poo tank is a common issue so I almost expect to work on it. Let us know what you decide to do.

 

[DennisG01]

If you can't find a solid bulkhead fitting to cover the hole, you could probably plug the bulkhead fitting with some pipe plugs... possibly needing a step down bushing first. Or maybe you could find a bulkhead fitting with the same threads as the sensor and just use the sensor as the plug?

A very good friend of mine plastic welded his wakeboard's ballast tank (I think it was about a 60g tank). It was even at a corner - your spot is easier and under much less stress. This was about 7 or 8 years ago. Yes, I think plastic welding is a good option - last I checked, they're not all that expensive, either.

The butane torch might be tough - you have really be careful to control the heat. I'm sure it could be done - just be really patient.

 

[SkunkBoat]

its on the top of the tank. clean it, sand it , cover the gap in silicone.

The groco sensor is a couple float sensors dangling by its wires. They snap off and then jam in the macerator.

 

[DennisG01]

Another option, since you have good access to the underside, is to make your own plate and gasket (like the existing plate). But here, you could use bolts/nuts since you can access it. A simple aluminum plate with gasket material (whether rubber or goop) would do it. I'd probably use goop and let it partially setup then gently squeeze it down with the plate/nuts&bolts... but not completely.

 

[Fixit]

being LDPE silicone or any sealant won't adhere. I do like the aluminum plate idea.... but I dislike the idea of having to go inside the tank to install it...

 

[Sardinia306Bimini]

being LDPE silicone or any sealant won't adhere. I do like the aluminum plate idea.... but I dislike the idea of having to go inside the tank to install it...

Correct, HDPE and LDPE are so slippery that adhesion is very limited and I understand that you won't like to get in the tank.

If it would be mine and considering that replacing it seems to be a easy task I would go this way except price for that would be stellar.
Also the steel plate on the upper side looks rather rusty so replacing all with a new tank and fittings would solve this as well and give you peace of mind.

In the search for a new fuel tank I stumbled over a company in Italy who build custom size fuel and water tanks out of thick HDPE sheets and they are high frequency welded, but unfortunately not for gasoline. That is what you probably found, if not you may do a search in US.

Chris

 

[SkunkBoat]

Correct, HDPE and LDPE are so slippery that adhesion is very limited and I understand that you won't like to get in the tank.

If it would be mine and considering that replacing it seems to be a easy task I would go this way except price for that would be stellar.
Also the steel plate on the upper side looks rather rusty so replacing all with a new tank and fittings would solve this as well and give you peace of mind.

In the search for a new fuel tank I stumbled over a company in Italy who build custom size fuel and water tanks out of thick HDPE sheets and they are high frequency welded, but unfortunately not for gasoline. That is what you probably found, if not you may do a search in US.

The big plate is red/brown very hard plastic its not rusty. There is a rubber gasket between it and the tank.
If the sensor is not working I would suggest pulling the pump and looking for loose pieces of the sensor inside the tank.
Eventually they will jam the pump if they haven't already been sucked out during a pumpout.

A Jabsco complete 10 gal tank setup is $1025. A complete Groco setup is probably a lot more since the pump alone goes for $900.
Then you add hoses and a valve and such...
It is very difficult (even painful) to work on these things. they are tucked away and the hoses go to vent loops that are unreachable. They were all installed before the top of the boat was connected to the hull.

The "leak" is on the top of the tank. So its just fumes you are trying to block. I'm just saying that sealing that with something and leaving the tank in place (the pump works)is way cheaper and easier.
I'm sure there is a sealant or putty or glue that will do what you need. JBWELD has to make something like that....

 

[DennisG01]

FYI, you can get better adhesion with sealants to HDPE by flame treating it. I've had decent success with that over the years - although I wouldn't consider it a permanent solution. However, in this case (and as Skunk pointed out), we're not looking for a big pressure-resisting seal. Meaning, good tape would "almost" work

Another method is to physically roughen the plastic - I have done cross-hatching with a razor blade. This gives some "tooth" for the sealant to grab onto. This method, with then letting the sealant partially setup, before plopping the "cover-up" plate on would probably be my choice. You have the ability to make a very wide "sealing area", as well. As I write this, I think I would actually use butyl rubber tape as the "sealant" under the cover plate. That should be a permanent solution... and with the plate thru-bolted, I wouldn't hesitate to cut a hole in the plate and install a bulkhead fitting in the cover plate. I think you could do that with the properly spaced thru-bolts and caulk/sealant as well - but butyl rubber is better.

Still another option is a LARGER bulkhead fitting and then size down with reducer bushing(s).

Anyways, the point is, there are multiple solutions to this issue and it's a pretty easy repair.

If you do go down the road of getting a new tank... check out Todd tanks. Much less expensive and they are a good company that makes their products right here in the USA.

 

[Fixit]

lol. I received a quote from my local Canadian plastics place. a 14x20x16" tank built from 3/8" hdpe came in at 1660$ CAD. ( that would be 20 gals, double the size of OEM)... there is just no way im going to spend that.
looks like im just going to seal up that split fitting and forget about it... part of me wants to just plumb it straight overboard, but I frequent too many small anchorages and beaches to do that with a decent conscience .

 

[DennisG01]

lol. I received a quote from my local Canadian plastics place. a 14x20x16" tank built from 3/8" hdpe came in at 1660$ CAD. ( that would be 20 gals, double the size of OEM)... there is just no way im going to spend that.
looks like im just going to seal up that split fitting and forget about it... part of me wants to just plumb it straight overboard, but I frequent too many small anchorages and beaches to do that with a decent conscience .

Yes, please don't! I'm not sure about Canada, but in the US it's illegal to discharge overboard unless you're "X" miles offshore.