Originally Posted by HopCar
Peg Hall will be along shortly to give you the definitive answer.
I've already given him what I consider to be the definitive answer on another site...I'll repost it here for y'all:
Doesn't really matter whether the tank is vertical or horizontal unless the vertical orientation would make the tank deeper than 20". What does matter is the locations of the fittings in the tank, simplicity of plumbing
it, and ability to have a short straight relatively horizontal 1" vent line ("standard" vent line installed in all off the shelf tanks is only 5/8").
I know you want to get this job done, but I wouldn't go with a Todd tank...there's a reason why they're so cheap
...you get what you pay for. My big toenail is thicker than the tank walls...not thick enough to support the weight of the contents (35 gallons weighs nearly 300 lbs!) without bulging. So you'd have to build a plywood
box to support it on all sides or the sides will bulge, which ultimately results in a cracked tank. "Fitting relocation kits" are not the best thing either...they often leak!
You haven't mentioned hoses, but I suspect you're going cheap and easy to get for that so you can "get 'er done now" too...which means it's gonna permeate before the summer is over. You haven't mentioned exactly where you want to put this tank either...that can make plumbing
and venting more of an issue than it needs to be.
You say you "need to finish this install"...why the rush? If you have a real deadline, not an artificial one because you just want to get the boat into the water, I suggest you spend $50 for a cheap portapotty to get you onto the water and buy you the time you need to do this job right...'cuz it's ALWAYS cheaper and easier to do anything right the first time than it is to do it over...and you WILL have to do this job over if you go the way you're starting out to go.