I’m upgrading our travel trailer black holding tank and realized that there’s not much information about this on the net (for some reason, probably everyone wants to sell new RV’s). So a useful non-controversial post! This is the first part of a x part series, following along the process.
First some important details you will need before embarking on this ‘adventure’ yourself. You will need to find the GAWR (Gross Axle Weight Rating) of your trailer, the GVWR (Gross Vehicle Weight Rating), tire rating (make sure total of all tires is equal or greater than GAWR). Then get your trailer weighed, ready for camping (gear packed, food, etc.), full propane, I would recommend empty holding tanks as we can calculate their weight(s).
Measure your holding tanks! This can be a tiresome process, however I feel it’s very important as you may find (as I did) that my TT black holding tank was listed as 12 gallons in the trailer specifications however the tank + 2′ of 3″ piping + the neck of the toilet only manage 6 gallon total! Manufacturers get away with this by simply stating ‘specifications subject to change’. In my case I found out that both the tank AND trailer manufacturers over stated the capacity.
On to my specifics. Our TT is a 16′ single axle trailer:
- GAWR: 3500#
- GVWR: 3850#
- Actual Weight: 2700#
- Actual Axle weight: 2250#
There are plenty of guides to properly weighing a trailer so I’ll not go into that here. The important thing is that I’ve got 2250# on my axle. Subtract that from the axle rating and you get 800#. The usual baseline for water weight is 8.34# per gallon, current setup is 6 gallons black, 12 gallon gray and 14 gallon fresh. That makes a total of 267# (rounded up) of potential liquid storage, subtract that from the 800# leaves 534 pounds to work with. NOTE that some of the weight may end up on the hitch, in my case all tanks are behind the axle so I’m just going to rely on axle capacity.
Knowing the above tells me I’ve got over 500# or about 64 gallons of weight handling to work with. That’s more than enough to upgrade to 25 gallons (adds about 150#), leaving a nice safety cushion.
Next step is to get accurate drawings of your tank. In my case the tank had the model number and manufacturer information (and 10 gal!) molded into it. Using that information I tracked down the current drawing
Note that the manufacturer downgraded it to “7 1/5 GAL” still an overstatement however at least closer. You can see on the image that it has ‘ears’ about 3″ tall by 1.5″ deep. These ‘ears’ turn out to be a very common mountain method, in my case one side mounted into the rear of the frame (basically the bumper rail) and the other side has a removable angle bracket bolted into the frame.
A trip under the trailer with a tape measure found that I could do 50″ side-side and 27″ fore-aft with a bit of room to spare. Then it’s off to find a new tank. Ameri-Kart is one of the bigger manufacturers, poking around there I found a 27 gallon tank that would fit easily. Ameri-Kart seems to deal primarily with wholesale, digging further I found an online seller Pelland Enterprises that deals directly with customers, AND had some of the fittings I needed to finish the project. In another case of manufacturer overstating, the tank is listed as 27 gallon on both websites, however when I ordered it was listed on the invoice as 25 gallon.. We’ll see what it’ll hold after installed..
So I ordered the tank, 1.5″ and 3″ flex rubber fittings (basically grommets for the toilet fitting and vent pipe), 4 sending units for the level sensor.. And then waited (takes a while to get the tanks made and shipped). Received everything else fairly quick, tank is due to arrive today! So far about $360 into the upgrade, not bad as that’s the bulk of cost (besides time).
While waiting I removed the old tank and did what prep work I could.
Only mistake so far, waiting to order until I removed the old tank. One of the places I was going to purchase from required detailed drawings for fittings so they can spin-weld them before shipping (I think the only choice for ABS tanks). Needless to say getting accurate measurements meant removing the old tank, so I waited just in case we wanted to go camping… Crossed my circuit I guess and didn’t remember that I’d be able to install the fittings in the PE tank so didn’t really need to wait.