SoBe,
I've often considered in researching carwashes with the objective similar to yours - not run the business, but still have the benefits. Having no prior experience nor specific technical knowledge, consider my message as sheer analytical observation. So here goes:
Taking into account the basic function of a car wash, manned or un-manned, you have a considerable amount of moving parts and tremendous amounts of water and chemical treatments. With these elements I imagine a considerable amount of deterioration to go along with that. This would probably lead to an accelerated depreciation of fixed assets and machinery and short life span for expensive equipment. In addition, I suspect the revenue generated by the business is predominately a cash basis, which may make it difficult to track and/or identify skimming from the register. Perhaps not of major concern, but a possible element none the less. In addition, the type of labor involved in operation of such a business is certainly not highly skilled, so I would imagine high turn over which could be detrimental to productivity and customer satisfaction. Lastly, but most importantly, the environmental impact of such a business I'm guessing will almost certainly depreciate the land value if the usage were to change as it would require clean up and perhaps remediation. In addition, with environmental impact becoming a greater concern you may be seeing this effect happen and evidenced by the increased inventory of such business on the market as owners are realizing larger and larger impact fees levied by state, county or federal entities.
Most of what I've previously described relates to the operations component, I'd like to shed a little light on the financials as well. In most municipalities, the water and sewer services are provided by public works. Water being the most consumed element in the operation, it's usage can be tracked on a per gallon basis. In addition, the consumption of water by the machinery can be calculated and is usually indicated in the the design specs from the manufacturer. By combining these factors you can calculate with fair accuracy the expected sales revenue (gallons used/#gallons per wash = # washes * cost per wash = total sales). From there work down your expenses, cost of water, other utilities, salaries, etc.
Finally, as I understand, triple net leases means the tenant is responsible for all maintenance, repairs and utilities. Even tax increases are passed through. Beyond that I don't know anything more about lease structures.
Good Luck
Glenn