[jennyJ]

Hi All...
I figured that I would keep everyone posted on a winter project that I am working on... The dreaded black water holding tank replacement on the 4000 Express.  If you are reading this, you are probably aware that the holding tank is a weak link in the overall excellence of the 4000 Express.  It is made from aluminum and it is located in a God-forsaken location in the boat that was NEVER meant to be serviced.  
The boat is "new" to me (two years) and I suspected I had a problem after the first year - I had no idea the problem was as bad as it was.  The tank was clearly leaking - and needed to be removed.  

This is work in progress and I will continue to keep you posted as the work progresses...

STEP 1.
I removed the access hatch (no brainer)
   

STEP 2. 
I cut out the remaining Teak and Holly flooring from the aft stateroom.  I used a multi-tool and cut all along the outside edge of the remaining floor.  I didn't want to disturb the teak and holly.  It was very well adhered and was not coming off - so I cut the fiberglass floor that it was glued to...
   
STEP 3.
I cut out the 3/4" subfloor that was below the Teak and Holly Floor.  This exposed as much of the tank as possible. 
       
STEP 4. 
I cut off the top of the tank with my Sawz-all.  (This is where the project gets kinda gross - actually BEYOND gross)  I needed to expose as much of the tank as possible and devise a way to get it out of the hole.  The tank needed to be "evacuated" as best as possible, so I used a Wet-dry vac to remove the remaining liquid and solids (BEYOND GROSS - but it had to be done.  PRO TIP - Wear a Tyvek suit, mask, eye protection and booties - you will thank me later.
   
STEP 5. 
Once I had the top off, I realized that the only way to remove the tank was to cut it into pieces from the inside.  I cut it using a grinding wheel, sawz-all and jig saw.  I needed to cut it into six pieces to get it out of the hole and remove it from the boat.
STEP 6.
The tank sits in a fiberglassed "well" which contains any "spill over" from the tank.  In my case - there was A LOT of "spill over" because several of the holes were on the bottom of the tank.  Contained in the "well" was a significant amount of liquids and solids which needed to be removed.  (I saved you the photos!)  This area was COMPLETELY cleaned and disinfected with gallons (yes gallons) of bleach.  The entire area was wiped clean until NO residue remained.  
   
STEP 7.
I dried the "well" completely overnight and went back to the boat the next day.  I was pleased to note the boat did not smell at all! The well was clean and dry.  I did have to throw out the wet dry vac however!

STEP 8.
I painted the well with White Rustoleam Top Side Paint.  Let it dry and came back the next day.
   

STEP 9.
I built a prototype tank out of 1/2" insulation board.  I wanted to maximize the tank size that would fit in the newly cut out hole.  I knew that I would not be able to get the 50 gallon storage tank back in the hole so I wanted to create a template box that would slip into the hole.  With this box, I figured that I could get a new tank manufactured.  The "perfect" size that I came up with was 42" x 19" x 11" - this would provide a 35 gallon replacement tank.  Basically, I figured I had a couple of options to make this new tank - I could go to a local welding shop and create one - or I could research the plastic route.  Two local welders provided prices in the $1,500-$2,000 range.  I thought this was a little steep - and frankly wasn't too excited to go back with an aluminum tank and risk future failure.  I found a non-corrosive linear polyethylene tank from Ronco Plastic.  The tank wasn't "Perfect" in size - but I can make it work.  The resulting tank is 40" x 20" x 10" and will contain 30 gallons.  Cost on this tank will be just a little under $500.  I am currently waiting for that tank to be delivered.          

That's all for now.  I will continue to update you when I receive the new tank and mount it in...

[dplunske@cwpm.net]

I have a 94 4000 express just wondering how you determined the tank was definitely leaking.

[jennyJ]

I have a 94 4000 express just wondering how you determined the tank was definitely leaking.

First it was the odor.  The back bedroom would get a foul smell after each flush.  I didn't think anything of it - its a boat afterall...Then there were traces of black water in the bilge after a long weekend.  The well which contained the tank began to overflow in the bilge.  So to confirm, I pumped the tank, filled it with water via the overboard discharge.  I could clearly see that the water was overflowing OUTSIDE of the tank.

[hiccup]

Yuck. Nice job and thanks for documenting. I have a 38 Open and while the black water tank is plastic and accessible in the engine room, they made the freshwater tank from welded aluminum and placed it under the cabin sole. Similar to your situation, if it leaks, the floor has to be cut up (and the teak/holly cannot be spared in this case). However, at least 38 Open owners don't have to deal with that filth. Hopefully you don't have nightmares over that!

[Richard.Janek]

Very nice job! I'm sure you saved money doing this yourself. Thanks for posting this

[Jack Aperio]

What a project. Thanks for documenting and posting this. I have a 1995 model and have read about the holding tank failure issues. I’m very interested if you believe yours was a corrosion problem or seam issue. In my opinion, I believe the problem could be with the venting. I have investigated mine extensively and concluded that even with a brand new vent filter the air can’t flow back into the tank at the same rate as the waste that is being removed. This scenario results with the aluminum holding tank pulling in on itself creating a loud bass drum sound. My guess is that an aluminum holding tank can only tolerate this so many times before it finally fails. I experience the same sound when the main VacuFlush head is used more than once within a minute or two. The extra air pushing into the tank can’t flow through the vent fast enough and pushes the tank sides out resulting with the same bass drum sound.

A good solution that worked for me was adding a “T” with a cap within the vent line between the holding tank and the vent filter. Simply remove the cap anytime you’re pumping out and allow unobstructed air into the tank. This solved the issue for me….but educating my guests about the double flush is still required.

[Hooper]

Ronco Plastics is a great company ! Glad to hear they saved you in this project. I've bought two difference water tanks from them and they are just all about quality.