Black Water Holding Tank

[Paul]

Time once again to change out the hoses on the black water holding tank. It seems that I get about 3-4 years out of these things then they start to emit a slight aroma that is a little less than pleasant. The problem exists mostly in the hose used for pumping the tank out. I believe this is due to the fact that the hose from the toilet to the tank is normally filled with rinse water however the pump out hose is always flooded with black water. What ever the reason, these hoses have to go.

In order to change these hoses on the F26 with the fiberglass cockpit you have to hang upside down in the engine bay, like a contortionist, pinned between the exhaust manifolds and the edge of the floor while working at arms length and blind to what you are doing. This is where the problem comes in for me. I've done this gob a few times before however as some of you may remember, I missed out on last boating season due to a surgery performed my neck in the early spring. Although things are looking pretty good for me now, doing this kind of job again is out of the question. So my options are either to hire someone to do the job for me (have someone else wrench on my boat ) or find another way to do it. I decided that it's time to make this boat easier for me to service.

Below is a picture of the engine bay with the fresh water tank under the floor on the left and the black water tank (that you can't even see) under the floor on the right.



Below is a picture of the hose arrangement on the black water tank.



My plan here is to replace both the black water tank and the fresh water tank with new ones that have the fittings in a more serviceable location such as at the inboard side on the top of the tank. The tanks will be fabricated from HDPE sheet and will have pipe couplers with down tubes welded into the top similar to the way hydraulic tanks are fabricated. This will allow the pump out hose to be full only when the tank is being pumped out and remain empty the rest of the time which should in turn reduce the frequency that it needs to be changed due to smell. I'm not sure which way to go at the tip of the down tube for the pump out hose. What I'm wondering is if an angled cut is good here or is a 90° fitting required? The toilet has a built in macerator so clogging at the tip of the down tube I believe should be unlikely. Any thoughts on this? I haven't done the design on these tanks yet so I'm open to suggestions.

As for changing these tanks, I'll have to remove the exhaust manifolds then the job should be fairly easy. I'll also take the opportunity to relocate the oil filter, AC water pump, strainer and fresh water pumps to a more serviceable location. I plan on having this boat for a long time to come so its important that the maintenance required remains within my physical capabilities.

[rickalan35]

Not sure, but I may have noticed a spec of dirt in that engine room ...... then again

[mikeandanne]

I think you are right,if you look real close and squint,,lol----- good grief that looks better than brand new------ I think if I was determined to use the down tube config the slight angle cut with the tip of the tube almost touching the bottom of the tank would work for me----- the tip touching would stop the vac from sucking the bottom of the tank up and the angle would keep it from clogging , I would try to avoid 90's ( restriction point and would be hard to clean out)----- maybe too much angle would not allow the tank to be evacuated fully though---- try to get at least a 3/4" to 1" vent and install a vacuum breaker in the tank----- marinas use way too much vacuum if not watched at pump out ----- I have a stainless reinforced tank that has been partially collapsed---- Mike

[Commissionpoint]

Not sure, but I may have noticed a spec of dirt in that engine room ...... then again

I dunno about that, but that sure is one pretty Merc 228. The lustre of the black paint is just breathtaking. I think I'd only like it better if it had stock Merc valve covers. I like the nod to Chevy, but you can get a Chavelle to put those on.

Anyhow, OP I think if you want to be done with the stinky pipe situation, you gotta stop using whatever it is that you are using there. I don't have any of my books at home to tell me when the head was replumbed last, but IIRC its been 12-14 years. No foulness at all.

Hopefully you can get that sorted. Replacing that every 3 or 4 years is way too frequent. I believe its a materials issue, and if you find the proper material this issue is a thing of the past. The stuff you have in there looks a lot more like tigerflex spa hose than tigerflex waste hose. You need the higher grade stuff thats more expensive. Again I don't have the spec here, but I am sure you can find it.

Because of the way its designed in your variant, what you need to do is get yours or someone elses kid or grandkid in that hole and tell them what to do for you. Thats where I started.

[Big D]

The bottom of the pick up tube should be really close to the bottom of the tank. Cut the bottom of the tube at about a 30 deg angle. If the hose doesn't have to go through many twists and turns, use the non-rigid ABS pipe that you can get at any home building center. It allows for some bending but not much. It won't permeate though. The more flexible the hose, the quicker it will permeate unless you buy the very high priced new tech stuff. If you do this right though, you shouldn't have any standing liquid in the hose which is the main cause of permeation in just a few years. Sealand sells discharge pick up tubes and tank relief valves. While you're at it, double the diameter of your vent hose and through hull fitting.

[Paul]

DIRT???

I think I'd only like it better if it had stock Merc valve covers. I like the nod to Chevy, but you can get a Chavelle to put those on.

Good guess on the engine, the block is actually a 350 from a '69 Chevelle. Tough casting.

As for the tank, it sounds like the angled down tubes are the way to go. Avoiding vacuum issues sounds like a good idea as well. I'll be sure to add a second baffle to the black water tank for extra support. The size of the vent hose is limited to the size vent filter that I have however I can always add a second hose and filter. I'll check out the Seland tubes as this may save me some work. The suction hose will have to be flexible but it sounds like a better grade of hose is in order.

Thanks for the suggestions gents.

[Commissionpoint]

I think I'd only like it better if it had stock Merc valve covers. I like the nod to Chevy, but you can get a Chavelle to put those on.

Good guess on the engine, the block is actually a 350 from a '69 Chevelle. Tough casting.

HOGWASH!!!!

Its a Merc!

(or it is now, and I mean that in the nicest way possible)

((thank the gods its isn't a 318))

[Big D]

....(thank the gods its isn't a 318))

Wait a minute, the black engines are easy to kill. 318s, not so much!
Couldn't resist, but you must have known that was coming after you opened the door

[prowlersfish]

....(thank the gods its isn't a 318))

Wait a minute, the black engines are easy to kill. 318s, not so much!
Couldn't resist, but you must have known that was coming after you opened the door

Chevy has it as far as the most common and easiest to get parts for . But nothing holds up over time like a 318 or 440 marine engine . In saltwater ford or Chevy don't even come close IMO and experience .

[Commissionpoint]

Couldn't resist, but you must have known that was coming after you opened the door

I did, and I was thinking of your big blues when I wrote it.

[Paul]

Well I finally got going on the fresh and black water tank replacement job. I bought 2 sheets of 1/4"x 4'x 8' HDPE plastic and cut them into the panel sizes required for the tanks and baffles. Both are identical 25 gal capacity tanks with the only difference being the fitting arrangement on the lids. I also bought some HDPE in 2" and 3 " diameter bar stock and had a local lathe shop make the required weld in fittings for me. This may have been more expensive a way to go than spin weld fittings found on most purchased tanks, but I've always found the spin weld fittings to be a little too flimsy for my liking.

Below is a picture of one of the Ø 3"x 1 1/2 NPT fitting.



This picture shows it welded in place in the lid of the water tank.



This picture shows me welding the water tank together. I did all of the external welding with larger welds than required for trimming / shaping at a later time.



This shows the tank after trimming the welds.



The baffle in the center of the tank was welded along the bottom and sides inside the tank. However to weld the top of the baffle, I had to cut beveled slots in the lid to expose the top edge of the baffle then plug welded it in two places. This can be seen in the picture below.



This picture shows the tank with the fittings assembled.



The last thing that I have to do the the water tank is weld on the flange style foot mount, then pressure test it for leaks.

I have the panels cut for the black water tank as well but have not started to assemble it yet. For the suction fittings on this tank, I had the lathe shop make me a weld in coupler which is tapped 1 1/2 NPT at one end and the other end is counter bored to accept a Ø 2" tube. I then had them bore some of the Ø 2" bar stock to have a 1 1/2 " ID. This gave me a very solid suction tube to work with. Below is a picture of the components.



This next picture shows the parts dry fitted together. The tube will be cut to length when the lid is fitted to the tank, then welded into the coupler.



That's about it for now. I'm hoping to start on the second tank this weekend and I'm planing on doing the installation early next month.

[mikeandanne]

Nice work,very talented to do all that on your own---- what type of equipment do you use for plastic welding----- on another note are those pics of GBM in the background ? --- Mike

[Paul]

Nice work,very talented to do all that on your own---- what type of equipment do you use for plastic welding----- on another note are those pics of GBM in the background ? --- Mike

Mike,

I use a hot gas tool with hand fed rod that I purchase by the roll. It uses nowhere near the same amount of heat but the process is similar to TIG welding metal. And yes, those pictures were taken at GBM.

[rickalan35]

Welding plastic............ yet another thing I know nothing about! Except for the sure fact that if I tried to do it, the end result would probably be one of my limbs somehow welded to the tank, like tar baby.

Great plan and very impressive workmanship, Paul.

ps Is that a drag bike on the wall behind you?

[larryeddington]

It is called hot air welding, been used for years to assemble certain plastic piping and is great for repairing cracked fairings from motorcycles that have not stayed upright. I have one but not the quality of the one the author has I do not think. Was wondering what brand he was using myself.

Paul sure does an excellent job!