Forum Discussion
JeffBett
Jun 18, 2008Explorer
I have been wanting to do a gray tank add-on mod since I bought our TT last year. Our upcoming vacation finally got me going on it. The existing gray tank was always to small, especially for 4 of us and 2 being female. I found a tank on E-Bay that would work. Bought some angle iron from the local metal supply store and went at it. Below is the before image, the only place I had to put a large enough tank to make it worth it was between the axles, the cheap tank on E-Bay fit perfect.
![](http://img511.imageshack.us/img511/4500/tankbeforera2.jpg)
Below is the after image from the rear looking towards the old tank. The axle was slightly in the way for a straight run of the pipe to connect to the existing pipe, so I played it safe and put in a flexible hose section at that point so there would not be any extra stress on the hard plastic pipe at the point.
![](http://img254.imageshack.us/img254/9152/tankaftergh6.jpg)
The Original tank claimed to be 36 gal but only held about 27, and I added 36 more. Tonight I did a test with 5 gallon buckets and the 2 held 62 gallons, that should help. I still need to add a vent hose. The guy at a local RV repair shop suggested I just run a little hose up into the wheel well, as long as it is higher then the tank. Right now it just has a vent hole drilled at the top edge.
My costs were:
$104 Tank $45 + 59 shipping
$33 Angle Iron
$18 plumbing parts
$155 Total
![](http://img511.imageshack.us/img511/4500/tankbeforera2.jpg)
Below is the after image from the rear looking towards the old tank. The axle was slightly in the way for a straight run of the pipe to connect to the existing pipe, so I played it safe and put in a flexible hose section at that point so there would not be any extra stress on the hard plastic pipe at the point.
![](http://img254.imageshack.us/img254/9152/tankaftergh6.jpg)
The Original tank claimed to be 36 gal but only held about 27, and I added 36 more. Tonight I did a test with 5 gallon buckets and the 2 held 62 gallons, that should help. I still need to add a vent hose. The guy at a local RV repair shop suggested I just run a little hose up into the wheel well, as long as it is higher then the tank. Right now it just has a vent hole drilled at the top edge.
My costs were:
$104 Tank $45 + 59 shipping
$33 Angle Iron
$18 plumbing parts
$155 Total
About Travel Trailer Group
44,025 PostsLatest Activity: Feb 06, 2025