I have seen guys with old bread trucks or chip trucks with detailing stuff in the back. A trailer lets you park it and use your vehicle for normal use as well. Remember the tax write off for business use of your car as well if you plan on reporting the income which on advice from my counselor I strongly suggest you do.
As for gravity, the pressure you get is proportional to the elevation of the water level. I forget but it is around 1 psi per foot of water or something and no I am not busting out my engineering books to look it up either. It would allow you to fill a bucket but it would have to be pretty high to rinse the top of a car.
55 gallon drums have two bungs in them that are threaded and companies make spigots for them to dispense the contents.
I would suggest looking into exterminator tanks mounted in trucks. They are plastic and would last longer.
As for gravity, the pressure you get is proportional to the elevation of the water level. I forget but it is around 1 psi per foot of water or something and no I am not busting out my engineering books to look it up either. It would allow you to fill a bucket but it would have to be pretty high to rinse the top of a car.
55 gallon drums have two bungs in them that are threaded and companies make spigots for them to dispense the contents.
I would suggest looking into exterminator tanks mounted in trucks. They are plastic and would last longer.