Help with Water Tank For Food Trailer

Hello, I am having trouble finding a water tank that fits our needs and thought someone here might have some advice. I am searching for a 28-30 gallon water tank to serve as a waste tank. because we are mounting it underneath the trailer, our dimensions are limited. the tank needs to be no deeper than 10", no wider than 22" and no longer than 40". Any help is greatly appreciated, thank you!

Check out ebay. Search grey water tanks or waste water tanks. I am also mounting mine underneath and I found a place in Adrian Michigan that has a lot of different sizes. I live close to there and was able to pick mine up but they do offer shipping. Good luck!

I have to ask will a tank that is 10" x 22" x 40" hold 28 - 30 gallons?

10x22x40 is 8800 cubic inches. 231 cu inches in a gallon so 10x22x40 would be 38 gallons. Our ideal tank would be 40x20x9 which would be 31 gallons

I don't think they make a 31 gallon tank. LOL But take your measurements and put them into the search engine of your choice and see what comes up. Or search the gallon range you mentioned. And last but not least change the size of your fresh water tank slightly so that the % will work with your local HD rules. That's what most builders end up doing.

Yes, keep in mind the requirement for your waste tank to be 15% greater than the fresh water tank.

This one ????  30 gal  ....40x20x10 http://www.plastic-mart.com/product/600/30-gallon-rectangle-poly-tank-rb424 

It seems that a lot of folks are mounting these HDPE tanks under their trucks/trailers to use as greywater tanks. Are you guys covering your tanks with some sort of protective barrier? I recently mounted my tank, and it seems pretty thin and flimsy, like it could spring a leak if a large-enough rock gets kicked up.
I am referring to a tank such as this: 
pplmotorhomes.com/parts/rv-pumps-water/rv-water-tanks-groupphoto.jpg
 

I second the motion on plastic-mart.com tanks. My 50-gal gray water tank came loose (it's embarrassing) and got dragged under the stepvan, pushed along by the rear wheels, for at least a few hundred yards while I was thinking "what is that peculiar noise". It did tear up the threaded fitting where the drain is, and there are some hairy looking gouges, but I re-mounted it (with angle iron and threaded rods this time) and it doesn't leak.
 
Polyethylene is extremely hard to fracture, a rock will not hurt it and will probably not even leave a mark.
 
[Edit: yeah, according to the respective sites the PPL Motorhomes tanks are 1/8" HDPE while the Plastic Mart ones are 1/4" to 3/8". --KH]

TamaleTrolley, 
 
Hahaha, wow...I'm sorry for laughing but that was certainly a good (if unplanned) durability test for your tank! Thanks for the input; I am starting to second-guess my sheet-aluminum shroud I was in the process of fabricating :)