If my measurements are correct, then the following diagram shows the location of all fittings required for a replacement black water tank:

The top and bottom fittings are 3″ pipe thread; the top is a flush mount, and the bottom protrudes so that it’s flush on the inside of the tank. The side fitting is 2″ pipe thread and will be placed as close to the top of the tank as possible (which is why there’s no measurement for that direction on the diagram).

I’ve ordered the tank from Marine Sanitation in Seattle, WA (marinesan.com). The tank should arrive in 2 weeks; you may wish to wait until I’ve confirmed the measurements before ordering your own! I’ll update this post with the results.

I thought I’d order a custom-shaped black water tank for the Westy, considering the placement of the downpipe relative to the wheel well (the down pipe is forward of the wheel well). I sent my diagram off to six places, got 2 responses, both around $600 – much more than I had anticipated.

So back to the drawing board! A bit of playing around with some wooden boards made me realize that I could lose 3 inches to clear the wheel well, and still fit a big rectangular tank. My local supplier has a 21″ x 21″ x 11.25″ tank that can squeeze into the space – that’s 20 gallons!

I do lose some storage in the back. I used to keep dirty boots in the little alcove between the door and the old black water tank, but the new tank will come right to the threshold. But that’s not a bad tradeoff for the larger capacity.

(Cardboard mockup of a 20G black water tank.)

(Mockup of a 20G black water tank, showing the 3″ space to the left required to clear the wheel well.)

My black water system has been giving me grief – a leaky gate valve under the tank, an improperly sealed inlet on the top, and a relatively small capacity all combined to force me to come up with a replacement.

I’m not a fan of the current setup (even if it was working well) for a few reasons:

• The capacity is too small. For a family of four, three days without dumping is pushing our luck. We often camp for three days and would prefer not to get nervous on the last day!
• The dump handle is inside the back doors. This is good for security, as it prevents accidental or malicious dumping, but it’s a pain to reach under the open back door and pull the handle while also holding the dump hose in place.
• The dump hose is too short. I have to back in to dump stations at crazy angles and get the corner of the van within a foot or two in order to get the hose in place.
• Tank level reporting is vague. The 4-LED display panel gives a rough idea, but I’d prefer to have an accurate readout of my tank level.
• Servicing is close to impossible. To replace the gate valve, you need to remove all of the Sikaflex sealant from the coupling below the van. To remove the inlet tube, you need a saw!

I plan on replacing the tank with a larger, custom-shaped tank. I have a request-for-quote in to George’s Custom Plastics in Tacoma, WA. A standard rectangular tank could be used, but not efficiently – the hole in the floor for the drain is forward of the back edge of the wheel well, so a rectangular tank would waste a lot of space. I’ve posted my planned shape with the pictures below.

More as the project progresses…